x/(b-a) = ?/(d-c) 不需要这么麻烦 直接这样就行： objBigBoxImage.style.left = -objFloatBox.offsetLeft/(objFloatBox.offsetWidth/objBigBox.offsetWidth) + "px"; objBigBoxImage.style.top = -objFloatBox.offsetTop/(objFloatBox.offsetHeight/objBigBox.offsetHeight) + "px";