diff --git a/deep_speech_2/tune.py b/deep_speech_2/tune.py
index 328d67a1197634e5f02ad0689056196a8904fc06..5dc44a86c72637124348b05b9e0bceb4801f5270 100644
--- a/deep_speech_2/tune.py
+++ b/deep_speech_2/tune.py
@@ -15,10 +15,10 @@ import utils
 
 parser = argparse.ArgumentParser(description=__doc__)
 parser.add_argument(
-    "--num_samples",
-    default=100,
+    "--batch_size",
+    default=128,
     type=int,
-    help="Number of samples for parameters tuning. (default: %(default)s)")
+    help="Minibatch size for parameters tuning. (default: %(default)s)")
 parser.add_argument(
     "--num_conv_layers",
     default=2,
@@ -51,7 +51,7 @@ parser.add_argument(
     help="Number of cpu threads for preprocessing data. (default: %(default)s)")
 parser.add_argument(
     "--num_processes_beam_search",
-    default=multiprocessing.cpu_count() // 2,
+    default=multiprocessing.cpu_count(),
     type=int,
     help="Number of cpu processes for beam search. (default: %(default)s)")
 parser.add_argument(
@@ -130,7 +130,12 @@ args = parser.parse_args()
 
 
 def tune():
-    """Tune parameters alpha and beta on one minibatch."""
+    """Tune parameters alpha and beta for the CTC beam search decoder
+    incrementally. The optimal parameters up to now would be output real time
+    at the end of each minibatch data, until all the development data is
+    taken into account. And the tuning process can be terminated at any time
+    as long as the two parameters get stable.
+    """
     if not args.num_alphas >= 0:
         raise ValueError("num_alphas must be non-negative!")
     if not args.num_betas >= 0:
@@ -144,14 +149,9 @@ def tune():
         num_threads=args.num_threads_data)
     batch_reader = data_generator.batch_reader_creator(
         manifest_path=args.tune_manifest_path,
-        batch_size=args.num_samples,
+        batch_size=args.batch_size,
         sortagrad=False,
         shuffle_method=None)
-    tune_data = batch_reader().next()
-    target_transcripts = [
-        ''.join([data_generator.vocab_list[token] for token in transcript])
-        for _, transcript in tune_data
-    ]
 
     ds2_model = DeepSpeech2Model(
         vocab_size=data_generator.vocab_size,
@@ -166,24 +166,44 @@ def tune():
     params_grid = [(alpha, beta) for alpha in cand_alphas
                    for beta in cand_betas]
 
-    ## tune parameters in loop
-    for alpha, beta in params_grid:
-        result_transcripts = ds2_model.infer_batch(
-            infer_data=tune_data,
-            decode_method='beam_search',
-            beam_alpha=alpha,
-            beam_beta=beta,
-            beam_size=args.beam_size,
-            cutoff_prob=args.cutoff_prob,
-            vocab_list=data_generator.vocab_list,
-            language_model_path=args.language_model_path,
-            num_processes=args.num_processes_beam_search)
-        wer_sum, num_ins = 0.0, 0
-        for target, result in zip(target_transcripts, result_transcripts):
-            wer_sum += wer(target, result)
-            num_ins += 1
-        print("alpha = %f\tbeta = %f\tWER = %f" %
-              (alpha, beta, wer_sum / num_ins))
+    wer_sum = [0.0 for i in xrange(len(params_grid))]
+    ave_wer = [0.0 for i in xrange(len(params_grid))]
+    num_ins = 0
+    num_batches = 0
+    ## incremental tuning parameters over multiple batches
+    for infer_data in batch_reader():
+        target_transcripts = [
+            ''.join([data_generator.vocab_list[token] for token in transcript])
+            for _, transcript in infer_data
+        ]
+
+        num_ins += len(target_transcripts)
+        # grid search
+        for index, (alpha, beta) in enumerate(params_grid):
+            result_transcripts = ds2_model.infer_batch(
+                infer_data=infer_data,
+                decode_method='beam_search',
+                beam_alpha=alpha,
+                beam_beta=beta,
+                beam_size=args.beam_size,
+                cutoff_prob=args.cutoff_prob,
+                vocab_list=data_generator.vocab_list,
+                language_model_path=args.language_model_path,
+                num_processes=args.num_processes_beam_search)
+
+            for target, result in zip(target_transcripts, result_transcripts):
+                wer_sum[index] += wer(target, result)
+            ave_wer[index] = wer_sum[index] / num_ins
+            print("alpha = %f, beta = %f, WER = %f" %
+                  (alpha, beta, ave_wer[index]))
+
+        # output on-line tuning result at the the end of current batch
+        ave_wer_min = min(ave_wer)
+        min_index = ave_wer.index(ave_wer_min)
+        print("Finish batch %d, optimal (alpha, beta, WER) = (%f, %f, %f)\n" %
+              (num_batches, params_grid[min_index][0],
+               params_grid[min_index][1], ave_wer_min))
+        num_batches += 1
 
 
 def main():