[button setImageEdgeInsets:UIEdgeInsetsMake(2, 70, 2,70 )];
[button setImageEdgeInsets:UIEdgeInsetsMake(<#CGFloat top#>, <#CGFloat left#>, <#CGFloat bottom#>, <#CGFloat right#>)]
上边距 左边距 下边距 右边距
原文:http://www.cnblogs.com/OIMM/p/5583897.html