diff --git a/paddle/strings/stringpiece.cc b/paddle/strings/stringpiece.cc
index ef46490fb1aaecbc8450b183fa4919f64fb97ba4..cc6d6a23f655622a94a5f474d22fe53f20ad5c5c 100644
--- a/paddle/strings/stringpiece.cc
+++ b/paddle/strings/stringpiece.cc
@@ -30,8 +30,8 @@ StringPiece::StringPiece(const char* d, size_t n) : data_(d), size_(n) {
         "StringPiece requires len to be 0 for NULL data");
 }
 
-StringPiece::StringPiece(const char* s) : data_(s), size_(strlen(s)) {
-  if (s == NULL) size_ = 0;
+StringPiece::StringPiece(const char* s) : data_(s) {
+  size_ = (s == NULL) ? 0 : strlen(s);
 }
 
 StringPiece::StringPiece(const std::string& s)
diff --git a/paddle/strings/stringpiece.h b/paddle/strings/stringpiece.h
index febb9036dbabba1d180bd1aeedcb665782dcdba9..f10b5eecf4316b42244e1f7ed3f7eb30e03a2191 100644
--- a/paddle/strings/stringpiece.h
+++ b/paddle/strings/stringpiece.h
@@ -40,14 +40,8 @@ public:
   StringPiece(const char* s);
   StringPiece(const std::string& s);
 
-  // For a string, cap() returns the size of storage and len()
-  // returns the currently used storage.  For a StringPiece these
-  // are the same value.
-  size_t cap() const { return size_; }
-  size_t len() const { return size_; }
-  size_t size() const { return size_; }
-
   const char* data() const { return data_; }
+  size_t len() const { return size_; }
 
   char operator[](size_t n) const {
     assert(n < len());
diff --git a/paddle/strings/stringpiece_test.cc b/paddle/strings/stringpiece_test.cc
index 79fc219a9c9056b9dd77ba6caa1de3ff136bb844..84ebc0ee032043829e956c5c0fac9f34a94f50a6 100644
--- a/paddle/strings/stringpiece_test.cc
+++ b/paddle/strings/stringpiece_test.cc
@@ -22,7 +22,6 @@ TEST(StringPiece, Construct) {
     paddle::StringPiece s;
     EXPECT_EQ(NULL, s.data());
     EXPECT_EQ(0U, s.len());
-    EXPECT_EQ(0U, s.cap());
   }
   {
     EXPECT_THROW([] { paddle::StringPiece s(NULL, 10000U); }(),
@@ -43,12 +42,10 @@ TEST(StringPiece, Construct) {
 TEST(StringPiece, CopyAndAssign) {
   paddle::StringPiece empty;
   EXPECT_EQ(0U, empty.len());
-  EXPECT_EQ(0U, empty.cap());
 
   paddle::StringPiece a("hello");
   paddle::StringPiece b = a;
   EXPECT_EQ(b.len(), strlen("hello"));
-  EXPECT_EQ(b.cap(), strlen("hello"));
   EXPECT_EQ(a, b);
 
   std::string storage("hello");
@@ -56,3 +53,25 @@ TEST(StringPiece, CopyAndAssign) {
   EXPECT_EQ(a, c);
   EXPECT_NE(a.data(), c.data());
 }
+
+TEST(StringPiece, Comparison) {
+  {
+    paddle::StringPiece a("hello");
+    paddle::StringPiece b("world");
+    EXPECT_TRUE(a != b);
+    EXPECT_FALSE(a == b);
+    EXPECT_TRUE(a < b);
+    EXPECT_TRUE(a <= b);
+    EXPECT_FALSE(a > b);
+    EXPECT_FALSE(a >= b);
+  }
+  {
+    paddle::StringPiece a, b;
+    EXPECT_TRUE(a == b);
+    EXPECT_FALSE(a != b);
+    EXPECT_FALSE(a < b);
+    EXPECT_FALSE(a > b);
+    EXPECT_TRUE(a <= b);
+    EXPECT_TRUE(a >= b);
+  }
+}