NSString *appleID = @"your app appleID";
    NSMutableURLRequest *request = [[NSMutableURLRequest alloc] init];
    [request setURL:[NSURL URLWithString:[NSString stringWithFormat:@"http://itunes.apple.com/lookup?id=%@",appleID]]];
    [request setHTTPMethod:@"GET"];
    NSData *returnData = [NSURLConnection sendSynchronousRequest:request returningResponse:nil error:nil];

 NSMutableDictionary *jsondata = [NSJSONSerialization JSONObjectWithData:returnData options:NSJSONReadingMutableLeaves error:nil];
    NSLog(@"jsondata===%@",jsondata);
    NSMutableArray *resultsArr = [jsondata objectForKey:@"results"];
    NSMutableDictionary *infodic = [resultsArr objectAtIndex:0];
    NSString *latestVersion = [infodic objectForKey:@"version"];
    NSString *trackViewUrl = [infodic objectForKey:@"trackViewUrl"];
    NSLog(@"%@",trackViewUrl);
    NSLog(@"latestVersion=%@",latestVersion);
    
    [[NSUserDefaults standardUserDefaults]setObject:trackViewUrl forKey:@"trackViewUrl"];
    NSLog(@"uurrll=%@",trackViewUrl);
    NSDictionary *infoDict = [[NSBundle mainBundle] infoDictionary];
    NSString *currentVersion = [infoDict objectForKey:@"CFBundleShortVersionString"];
    NSLog(@"当前版本号是%@",currentVersion);
    NSLog(@"doublecurrent=%@",currentVersion);
    if ([currentVersion isEqualToString:latestVersion]) {
        NSLog(@"版本相同 不用更新");
        [[NSUserDefaults standardUserDefaults] removeObjectForKey:@"updateVersion"];
        [[NSUserDefaults standardUserDefaults] setObject:@"no" forKey:@"updateVersion"];
    }else
    {   NSArray * newVerAry = [latestVersion componentsSeparatedByString:@"."];
        NSArray * curVerAry = [currentVersion componentsSeparatedByString:@"."];
        for (int i = 0; i < [newVerAry count] || i < [curVerAry count]; i++)
        {
            int newSubVer, curSubVer;
            // 如果子版本号数不足，作为0处理
            if (i >= [newVerAry count])
            {
                newSubVer = 0;
            }
            else
            {
                newSubVer = [[newVerAry objectAtIndex:i] intValue];
            }
            
            if( i >= [curVerAry count])
            {
                curSubVer = 0;
            }
            else
            {
                curSubVer = [[curVerAry objectAtIndex:i] intValue];
            }
            
            if( newSubVer > curSubVer)
            {
                NSLog(@"当前版本低 ，需要更新");
                [[NSUserDefaults standardUserDefaults] removeObjectForKey:@"updateVersion"];
                [[NSUserDefaults standardUserDefaults] setObject:@"yes" forKey:@"updateVersion"];
                NSLog(@"version == yes");
                return;
            }
            else if( newSubVer < curSubVer)
            {
                NSLog(@"当前版本高 不需要更新");
                [[NSUserDefaults standardUserDefaults] removeObjectForKey:@"updateVersion"];
                [[NSUserDefaults standardUserDefaults] setObject:@"no" forKey:@"updateVersion"];
                return;
            }
        }
        
    }

上边是完整的判断代码，判断结果保存在UserDefaults里边，“yes”为有新版本，“no”为没有新版本。
该方法适用于APP版本为1.0.0这种格式。