var td='<td width=463 valign=top style="
width:347.3000pt; padding:0.0000pt 5.4000pt 0.0000pt 5.4000pt ; border-left:31.8750pt none rgb(255,255,255); mso-border-left-alt:31.8750pt none rgb(255,255,255); border-right:0.5000pt solid rgb(0,0,0); mso-border-right-alt:0.5000pt solid rgb(0,0,0); border-top:31.8750pt none rgb(255,255,255); mso-border-top-alt:31.8750pt none rgb(255,255,255); border-bottom:0.5000pt solid rgb(0,0,0); mso-border-bottom-alt:0.5000pt solid rgb(0,0,0); " >保留我<td>';
//注意有时style后又换行或回车
//最终得到要求如下
td="<td width=463 valign=top>保留我</td>";
------解决方案--------------------
td=td.replace(/\s+style=[^>]+/,'');
alert(td);