转载自：http://www.cnblogs.com/maxfong/p/3375167.html

iOS7之前的UI为：

而在iOS7中，由于设计方面的原因，使得UI变为:

修改的方法重写UINavigationItem的setLeftBarButtonItem和setRightBarButtonItem方法，使之与之前版本兼容；

代码如下：

@interface UINavigationItem (margin)

@end

@implementation UINavigationItem (margin)

#if __ipHONE_OS_VERSION_MAX_ALLOWED > __IPHONE_6_1
- (void)setLeftBarButtonItem:(UIBarButtonItem *)_leftBarButtonItem
{
    if ([[[UIDevice currentDevice] systemVersion] floatValue] >= 7.0)
    {
        UIBarButtonItem *negativeSeperator = [[UIBarButtonItem alloc] initWithBarButtonSystemItem:UIBarButtonSystemItemFixedSpace target:nil action:nil];
        negativeSeperator.width = -12;
        
        if (_leftBarButtonItem)
        {
            [self setLeftBarButtonItems:@[negativeSeperator, _leftBarButtonItem]];
        }
        else
        {
            [self setLeftBarButtonItems:@[negativeSeperator]];
        }
        [negativeSeperator release];
    }
    else
    {
        [self setLeftBarButtonItem:_leftBarButtonItem animated:NO];
    }
}

- (void)setRightBarButtonItem:(UIBarButtonItem *)_rightBarButtonItem
{
    if ([[[UIDevice currentDevice] systemVersion] floatValue] >= 7.0)
    {
        UIBarButtonItem *negativeSeperator = [[UIBarButtonItem alloc] initWithBarButtonSystemItem:UIBarButtonSystemItemFixedSpace target:nil action:nil];
        negativeSeperator.width = -12;
        
        if (_rightBarButtonItem)
        {
            [self setRightBarButtonItems:@[negativeSeperator, _rightBarButtonItem]];
        }
        else
        {
            [self setRightBarButtonItems:@[negativeSeperator]];
        }
        [negativeSeperator release];
    }
    else
    {
        [self setRightBarButtonItem:_rightBarButtonItem animated:NO];
    }
}

#endif
@end

项目源码不做任何修改，问题解决；

添加Button：

UIBarButtonItem *leftBarItem = [[UIBarButtonItem alloc] initWithCustomView:btnBack];
self.navigationItem.leftBarButtonItem = leftBarItem;
[leftBarItem release];