diff --git a/library/src/main/java/com/liulishuo/filedownloader/download/DownloadStatusCallback.java b/library/src/main/java/com/liulishuo/filedownloader/download/DownloadStatusCallback.java
index 617165d7..4fa68d28 100644
--- a/library/src/main/java/com/liulishuo/filedownloader/download/DownloadStatusCallback.java
+++ b/library/src/main/java/com/liulishuo/filedownloader/download/DownloadStatusCallback.java
@@ -37,6 +37,7 @@
 
 import java.io.File;
 import java.io.IOException;
+import java.util.concurrent.atomic.AtomicLong;
 
 import static com.liulishuo.filedownloader.download.FetchDataTask.BUFFER_SIZE;
 import static com.liulishuo.filedownloader.model.FileDownloadModel.TOTAL_VALUE_IN_CHUNKED_RESOURCE;
@@ -121,14 +122,12 @@ void onMultiConnection() {
 
     private volatile long lastCallbackTimestamp = 0;
 
-    private volatile long callbackIncreaseBuffer = 0;
-    private final Object increaseLock = new Object();
+    private final AtomicLong callbackIncreaseBuffer = new AtomicLong();
 
     void onProgress(long increaseBytes) {
-        synchronized (increaseLock) {
-            this.callbackIncreaseBuffer += increaseBytes;
-            model.setSoFar(model.getSoFar() + increaseBytes);
-        }
+
+        callbackIncreaseBuffer.addAndGet(increaseBytes);
+        model.increaseSoFar(increaseBytes);
 
         model.setStatus(FileDownloadStatus.progress);
 
@@ -146,10 +145,8 @@ void onProgress(long increaseBytes) {
     }
 
     void onRetry(Exception exception, int remainRetryTimes, long invalidIncreaseBytes) {
-        synchronized (increaseLock) {
-            this.callbackIncreaseBuffer = 0;
-            model.setSoFar(model.getSoFar() - invalidIncreaseBytes);
-        }
+        this.callbackIncreaseBuffer.set(0);
+        model.increaseSoFar(-invalidIncreaseBytes);
 
         if (handler == null) {
             // direct
@@ -372,9 +369,7 @@ private void handleProgress(final long now,
         if (isNeedCallbackToUser) {
             lastCallbackTimestamp = now;
             onStatusChanged(FileDownloadStatus.progress);
-            synchronized (increaseLock) {
-                callbackIncreaseBuffer = 0;
-            }
+            callbackIncreaseBuffer.set(0);
         }
     }
 
@@ -460,7 +455,7 @@ private boolean isNeedCallbackToUser(final long now) {
         final long callbackTimeDelta = now - lastCallbackTimestamp;
 
 
-        return (callbackMinIntervalBytes != NO_ANY_PROGRESS_CALLBACK && callbackIncreaseBuffer >= callbackMinIntervalBytes)
+        return (callbackMinIntervalBytes != NO_ANY_PROGRESS_CALLBACK && callbackIncreaseBuffer.get() >= callbackMinIntervalBytes)
                 && (callbackTimeDelta >= callbackProgressMinInterval);
     }
 
diff --git a/library/src/main/java/com/liulishuo/filedownloader/model/FileDownloadModel.java b/library/src/main/java/com/liulishuo/filedownloader/model/FileDownloadModel.java
index cd630dcd..70921c5a 100644
--- a/library/src/main/java/com/liulishuo/filedownloader/model/FileDownloadModel.java
+++ b/library/src/main/java/com/liulishuo/filedownloader/model/FileDownloadModel.java
@@ -24,6 +24,7 @@
 import com.liulishuo.filedownloader.util.FileDownloadUtils;
 
 import java.io.File;
+import java.util.concurrent.atomic.AtomicLong;
 
 /**
  * The model of the downloading task will be used in the filedownloader database.
@@ -58,7 +59,7 @@ public class FileDownloadModel implements Parcelable {
     private byte status;
     public final static String STATUS = "status";
 
-    private long soFar;
+    private final AtomicLong soFar;
     private long total;
 
     public final static String SOFAR = "sofar";
@@ -92,7 +93,11 @@ public void setStatus(byte status) {
     }
 
     public void setSoFar(long soFar) {
-        this.soFar = soFar;
+        this.soFar.set(soFar);
+    }
+
+    public void increaseSoFar(long increaseBytes){
+        this.soFar.addAndGet(increaseBytes);
     }
 
     public void setTotal(long total) {
@@ -145,7 +150,7 @@ public byte getStatus() {
     }
 
     public long getSoFar() {
-        return soFar;
+        return soFar.get();
     }
 
     public long getTotal() {
@@ -274,7 +279,7 @@ public void writeToParcel(Parcel dest, int flags) {
         dest.writeByte(this.pathAsDirectory ? (byte) 1 : (byte) 0);
         dest.writeString(this.filename);
         dest.writeByte(this.status);
-        dest.writeLong(this.soFar);
+        dest.writeLong(this.soFar.get());
         dest.writeLong(this.total);
         dest.writeString(this.errMsg);
         dest.writeString(this.eTag);
@@ -283,6 +288,7 @@ public void writeToParcel(Parcel dest, int flags) {
     }
 
     public FileDownloadModel() {
+        this.soFar = new AtomicLong();
     }
 
     protected FileDownloadModel(Parcel in) {
@@ -292,7 +298,7 @@ protected FileDownloadModel(Parcel in) {
         this.pathAsDirectory = in.readByte() != 0;
         this.filename = in.readString();
         this.status = in.readByte();
-        this.soFar = in.readLong();
+        this.soFar = new AtomicLong(in.readLong());
         this.total = in.readLong();
         this.errMsg = in.readString();
         this.eTag = in.readString();