diff --git a/.travis.yml b/.travis.yml
index 6e89066..15c6111 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -1,4 +1,5 @@
 language: objective-c
 xcode_project: QiniuSDK.xcodeproj
 xcode_scheme: QiniuSDKTests
-xcode_sdk: iphonesimulator7.0
+xcode_sdk:
+  - iphonesimulator7.1
diff --git a/QiniuSDK.xcodeproj/project.pbxproj b/QiniuSDK.xcodeproj/project.pbxproj
index 98c475b..5d9dbfe 100644
--- a/QiniuSDK.xcodeproj/project.pbxproj
+++ b/QiniuSDK.xcodeproj/project.pbxproj
@@ -393,7 +393,7 @@
 				GCC_WARN_UNINITIALIZED_AUTOS = YES;
 				GCC_WARN_UNUSED_FUNCTION = YES;
 				GCC_WARN_UNUSED_VARIABLE = YES;
-				IPHONEOS_DEPLOYMENT_TARGET = 7.0;
+				IPHONEOS_DEPLOYMENT_TARGET = 6.1;
 				ONLY_ACTIVE_ARCH = YES;
 				SDKROOT = iphoneos;
 			};
@@ -424,7 +424,7 @@
 				GCC_WARN_UNINITIALIZED_AUTOS = YES;
 				GCC_WARN_UNUSED_FUNCTION = YES;
 				GCC_WARN_UNUSED_VARIABLE = YES;
-				IPHONEOS_DEPLOYMENT_TARGET = 7.0;
+				IPHONEOS_DEPLOYMENT_TARGET = 6.1;
 				SDKROOT = iphoneos;
 				VALIDATE_PRODUCT = YES;
 			};
diff --git a/QiniuSDK/QiniuHttpClient.m b/QiniuSDK/QiniuHttpClient.m
index 1b8f7c7..a6e8da5 100644
--- a/QiniuSDK/QiniuHttpClient.m
+++ b/QiniuSDK/QiniuHttpClient.m
@@ -31,17 +31,17 @@ - (AFHTTPRequestOperation *)uploadFile:(NSString *)filePath
                                 uphost:(NSString *)uphost
                               progress:(void (^)(float percent))progressBlock
                               complete:(QNObjectResultBlock)complete{
-    
+
     NSParameterAssert(filePath);
     NSParameterAssert(token);
     NSError *error = nil;
     [[[NSFileManager defaultManager] attributesOfItemAtPath:filePath error:&error] fileSize];
-    
+
     if (error) {
         complete(nil,error);
         return nil;
     }
-    
+
     NSData *data = [NSData dataWithContentsOfFile:filePath];
     return [self uploadFileData:data
                             key:key
@@ -62,7 +62,7 @@ - (AFHTTPRequestOperation *)uploadFileData:(NSData *)data
 
     NSParameterAssert(data);
     NSParameterAssert(token);
-    
+
     NSMutableDictionary *parameters = [NSMutableDictionary dictionary];
 
     if (key && ![key isEqualToString:kQiniuUndefinedKey]) {
@@ -73,7 +73,7 @@ - (AFHTTPRequestOperation *)uploadFileData:(NSData *)data
     }
 
     parameters[@"token"] = token;
-    
+
     if (extra) {
         [parameters addEntriesFromDictionary:extra.convertToPostParams];
     }
@@ -87,7 +87,7 @@ - (AFHTTPRequestOperation *)uploadFileData:(NSData *)data
                                                                                 URLString:uphost
                                                                                parameters:parameters
                                                                 constructingBodyWithBlock:^(id<AFMultipartFormData> formData) {
-                                                                    
+
                                                                     [formData appendPartWithFileData:data
                                                                                                 name:@"file"
                                                                                             fileName:key
@@ -129,7 +129,7 @@ @implementation QiniuPutExtra
 - (NSDictionary *)convertToPostParams{
     NSMutableDictionary *params = [NSMutableDictionary dictionaryWithDictionary:self.params];
     if (self.checkCrc == 1) {
-        params[@"crc32"] = [NSString stringWithFormat:@"%ld", self.crc32];
+        params[@"crc32"] = [NSString stringWithFormat:@"%u", (unsigned int)self.crc32];
     }
     return params;
 }
diff --git a/QiniuSDK/QiniuResumableClient.m b/QiniuSDK/QiniuResumableClient.m
index e2f4c1b..80759c8 100644
--- a/QiniuSDK/QiniuResumableClient.m
+++ b/QiniuSDK/QiniuResumableClient.m
@@ -170,12 +170,7 @@ - (void)blockPut:(NSData *)mappedData
 
 + (NSString *)encode:(NSString *)str
 {
-    str = [[str dataUsingEncoding:NSUTF8StringEncoding] base64EncodedStringWithOptions:0];
-
-    // is there other methed?
-    str = [str stringByReplacingOccurrencesOfString:@"+" withString:@"-"];
-    str = [str stringByReplacingOccurrencesOfString:@"/" withString:@"_"];
-    return str;
+    return urlSafeBase64String(str);
 }
 
 - (void)mkfile:(NSString *)key
diff --git a/QiniuSDK/QiniuUtils.h b/QiniuSDK/QiniuUtils.h
index 41381db..eab28b5 100644
--- a/QiniuSDK/QiniuUtils.h
+++ b/QiniuSDK/QiniuUtils.h
@@ -11,6 +11,7 @@
 typedef void (^QNProgress)(float percent);
 typedef void (^QNComplete)(AFHTTPRequestOperation *operation, NSError *error);
 
+NSString *urlSafeBase64String(NSString *sourceString);
 
 NSError *qiniuError(int errorCode, NSString *errorDescription);
 
diff --git a/QiniuSDK/QiniuUtils.m b/QiniuSDK/QiniuUtils.m
index f35216d..70e9f9f 100644
--- a/QiniuSDK/QiniuUtils.m
+++ b/QiniuSDK/QiniuUtils.m
@@ -13,6 +13,35 @@
 #define kQiniuErrorKey     @"error"
 #define kQiniuErrorDomain  @"QiniuErrorDomain"
 
+NSString *urlSafeBase64String(NSString *sourceString) {
+    NSData *data = [NSData dataWithBytes:[sourceString UTF8String] length:[sourceString lengthOfBytesUsingEncoding:NSUTF8StringEncoding]];
+    NSUInteger length = [data length];
+    NSMutableData *mutableData = [NSMutableData dataWithLength:((length + 2) / 3) * 4];
+
+    uint8_t *input = (uint8_t *)[data bytes];
+    uint8_t *output = (uint8_t *)[mutableData mutableBytes];
+
+    for (NSUInteger i = 0; i < length; i += 3) {
+        NSUInteger value = 0;
+        for (NSUInteger j = i; j < (i + 3); j++) {
+            value <<= 8;
+            if (j < length) {
+                value |= (0xFF & input[j]);
+            }
+        }
+
+        static uint8_t const kAFBase64EncodingTable[] = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789-_";
+
+        NSUInteger idx = (i / 3) * 4;
+        output[idx + 0] = kAFBase64EncodingTable[(value >> 18) & 0x3F];
+        output[idx + 1] = kAFBase64EncodingTable[(value >> 12) & 0x3F];
+        output[idx + 2] = (i + 1) < length ? kAFBase64EncodingTable[(value >> 6)  & 0x3F] : '=';
+        output[idx + 3] = (i + 2) < length ? kAFBase64EncodingTable[(value >> 0)  & 0x3F] : '=';
+    }
+
+    return [[NSString alloc] initWithData:mutableData encoding:NSASCIIStringEncoding];
+}
+
 NSError *qiniuError(int errorCode, NSString *errorDescription) {
     return [NSError errorWithDomain:kQiniuErrorDomain code:errorCode userInfo:[NSDictionary dictionaryWithObject:errorDescription forKey:kQiniuErrorKey]];
 }