#centerDIV { height: 550px; width: 100%; } #mainDIV { height: 100%; border: 1px solid #F00; margin-left: 102px; } #leftDIV { float: left; width: 100px; height: 100%; border: 1px solid #F00; } <div id="centerDIV"> <div id="leftDIV"></div> <div id="mainDIV"></div> </div>
左侧leftDIV的float:left;width固定,右侧的mainDIV用margin-left