diff --git a/cell.go b/cell.go
index 6788daf2c6164e6f7da01416789582cf84b493c7..ecfc5cae74e6d8a6361774c82979853150629d2c 100644
--- a/cell.go
+++ b/cell.go
@@ -7,7 +7,7 @@ import (
 )
 
 // GetCellValue provide function get value from cell by given sheet index and axis in XLSX file
-func GetCellValue(file []FileList, sheet string, axis string) string {
+func GetCellValue(file map[string]string, sheet string, axis string) string {
 	axis = strings.ToUpper(axis)
 	var xlsx xlsxWorksheet
 	row := getRowIndex(axis)
diff --git a/excelize.go b/excelize.go
index 6da86395b1644f0613de6f7b96157715100deeb8..2dd62d3a66c8ff4242f03200a7c6412769abd11e 100644
--- a/excelize.go
+++ b/excelize.go
@@ -17,7 +17,7 @@ type FileList struct {
 
 // OpenFile take the name of an XLSX file and returns a populated
 // xlsx.File struct for it.
-func OpenFile(filename string) (file []FileList, err error) {
+func OpenFile(filename string) (file map[string]string, err error) {
 	var f *zip.ReadCloser
 	f, err = zip.OpenReader(filename)
 	if err != nil {
@@ -28,7 +28,7 @@ func OpenFile(filename string) (file []FileList, err error) {
 }
 
 // SetCellInt provide function to set int type value of a cell
-func SetCellInt(file []FileList, sheet string, axis string, value int) []FileList {
+func SetCellInt(file map[string]string, sheet string, axis string, value int) map[string]string {
 	axis = strings.ToUpper(axis)
 	var xlsx xlsxWorksheet
 	col := getColIndex(axis)
@@ -58,7 +58,7 @@ func SetCellInt(file []FileList, sheet string, axis string, value int) []FileLis
 }
 
 // SetCellStr provide function to set string type value of a cell
-func SetCellStr(file []FileList, sheet string, axis string, value string) []FileList {
+func SetCellStr(file map[string]string, sheet string, axis string, value string) map[string]string {
 	axis = strings.ToUpper(axis)
 	var xlsx xlsxWorksheet
 	col := getColIndex(axis)
diff --git a/file.go b/file.go
index d30ffa215dde1f013db77a5a9354e198cb2b43a6..a25d66dec1147f05b0560bc1e1fa6aa7bb385242 100644
--- a/file.go
+++ b/file.go
@@ -9,8 +9,8 @@ import (
 // CreateFile provide function to create new file by default template
 // For example:
 // xlsx := CreateFile()
-func CreateFile() []FileList {
-	var file []FileList
+func CreateFile() map[string]string {
+	file := make(map[string]string)
 	file = saveFileList(file, `_rels/.rels`, templateRels)
 	file = saveFileList(file, `docProps/app.xml`, templateDocpropsApp)
 	file = saveFileList(file, `docProps/core.xml`, templateDocpropsCore)
@@ -24,15 +24,15 @@ func CreateFile() []FileList {
 }
 
 // Save after create or update to an xlsx file at the provided path.
-func Save(files []FileList, name string) error {
+func Save(files map[string]string, name string) error {
 	buf := new(bytes.Buffer)
 	w := zip.NewWriter(buf)
-	for _, file := range files {
-		f, err := w.Create(file.Key)
+	for path, content := range files {
+		f, err := w.Create(path)
 		if err != nil {
 			return err
 		}
-		_, err = f.Write([]byte(file.Value))
+		_, err = f.Write([]byte(content))
 		if err != nil {
 			return err
 		}
diff --git a/lib.go b/lib.go
index 93234118d2d26396793847fa43ef010431680444..7147424f42f94c0189f126d1a0614cd7dbac760e 100644
--- a/lib.go
+++ b/lib.go
@@ -14,51 +14,32 @@ import (
 // ReadZip takes a pointer to a zip.ReadCloser and returns a
 // xlsx.File struct populated with its contents. In most cases
 // ReadZip is not used directly, but is called internally by OpenFile.
-func ReadZip(f *zip.ReadCloser) ([]FileList, error) {
+func ReadZip(f *zip.ReadCloser) (map[string]string, error) {
 	defer f.Close()
 	return ReadZipReader(&f.Reader)
 }
 
 // ReadZipReader can be used to read an XLSX in memory without
 // touching the filesystem.
-func ReadZipReader(r *zip.Reader) ([]FileList, error) {
-	var fileList []FileList
+func ReadZipReader(r *zip.Reader) (map[string]string, error) {
+	fileList := make(map[string]string)
 	for _, v := range r.File {
-		singleFile := FileList{
-			Key:   v.Name,
-			Value: readFile(v),
-		}
-		fileList = append(fileList, singleFile)
+		fileList[v.Name] = readFile(v)
 	}
 	return fileList, nil
 }
 
 // Read XML content as string and replace drawing property in XML namespace of sheet
-func readXML(files []FileList, name string) string {
-	for _, file := range files {
-		if file.Key == name {
-			return strings.Replace(file.Value, "<drawing r:id=", "<drawing rid=", -1)
-		}
+func readXML(files map[string]string, name string) string {
+	if content, ok := files[name]; ok {
+		return strings.Replace(content, "<drawing r:id=", "<drawing rid=", -1)
 	}
 	return ``
 }
 
 // Update given file content in file list of XLSX
-func saveFileList(files []FileList, name string, content string) []FileList {
-	for k, v := range files {
-		if v.Key == name {
-			files = files[:k+copy(files[k:], files[k+1:])]
-			files = append(files, FileList{
-				Key:   name,
-				Value: XMLHeader + content,
-			})
-			return files
-		}
-	}
-	files = append(files, FileList{
-		Key:   name,
-		Value: XMLHeader + content,
-	})
+func saveFileList(files map[string]string, name string, content string) map[string]string {
+	files[name] = XMLHeader + content
 	return files
 }
 
diff --git a/sheet.go b/sheet.go
index eb8c291979fc8099466e38a5f63832ff5493f714..5ff2120089eed721693f0d1b59e6d79c7ff6ff55 100644
--- a/sheet.go
+++ b/sheet.go
@@ -11,7 +11,7 @@ import (
 // NewSheet provice function to greate a new sheet by given index, when
 //  creating a new XLSX file, the default sheet will be create, when you
 //  create a new file, you need to ensure that the index is continuous.
-func NewSheet(file []FileList, index int, name string) []FileList {
+func NewSheet(file map[string]string, index int, name string) map[string]string {
 	// Update docProps/app.xml
 	file = setAppXML(file)
 	// Update [Content_Types].xml
@@ -26,7 +26,7 @@ func NewSheet(file []FileList, index int, name string) []FileList {
 }
 
 // Read and update property of contents type of XLSX
-func setContentTypes(file []FileList, index int) []FileList {
+func setContentTypes(file map[string]string, index int) map[string]string {
 	var content xlsxTypes
 	xml.Unmarshal([]byte(readXML(file, `[Content_Types].xml`)), &content)
 	content.Overrides = append(content.Overrides, xlsxOverride{
@@ -41,7 +41,7 @@ func setContentTypes(file []FileList, index int) []FileList {
 }
 
 // Update sheet property by given index
-func setSheet(file []FileList, index int) []FileList {
+func setSheet(file map[string]string, index int) map[string]string {
 	var xlsx xlsxWorksheet
 	xlsx.Dimension.Ref = "A1"
 	xlsx.SheetViews.SheetView = append(xlsx.SheetViews.SheetView, xlsxSheetView{
@@ -56,7 +56,7 @@ func setSheet(file []FileList, index int) []FileList {
 }
 
 // Update workbook property of XLSX
-func setWorkbook(file []FileList, index int, name string) []FileList {
+func setWorkbook(file map[string]string, index int, name string) map[string]string {
 	var content xlsxWorkbook
 	xml.Unmarshal([]byte(readXML(file, `xl/workbook.xml`)), &content)
 
@@ -75,14 +75,14 @@ func setWorkbook(file []FileList, index int, name string) []FileList {
 }
 
 // Read and unmarshal workbook relationships of XLSX
-func readXlsxWorkbookRels(file []FileList) xlsxWorkbookRels {
+func readXlsxWorkbookRels(file map[string]string) xlsxWorkbookRels {
 	var content xlsxWorkbookRels
 	xml.Unmarshal([]byte(readXML(file, `xl/_rels/workbook.xml.rels`)), &content)
 	return content
 }
 
 // Update workbook relationships property of XLSX
-func addXlsxWorkbookRels(file []FileList, sheet int) []FileList {
+func addXlsxWorkbookRels(file map[string]string, sheet int) map[string]string {
 	content := readXlsxWorkbookRels(file)
 	rID := len(content.Relationships) + 1
 	ID := bytes.Buffer{}
@@ -105,7 +105,7 @@ func addXlsxWorkbookRels(file []FileList, sheet int) []FileList {
 }
 
 // Update docProps/app.xml file of XML
-func setAppXML(file []FileList) []FileList {
+func setAppXML(file map[string]string) map[string]string {
 	return saveFileList(file, `docProps/app.xml`, templateDocpropsApp)
 }
 
@@ -134,7 +134,7 @@ func replaceRelationshipsID(workbookMarshal string) string {
 }
 
 // SetActiveSheet provide function to set default active sheet of XLSX by given index
-func SetActiveSheet(file []FileList, index int) []FileList {
+func SetActiveSheet(file map[string]string, index int) map[string]string {
 	var content xlsxWorkbook
 	if index < 1 {
 		index = 1