一，如果该元素没有绝对／相对定位，则会把td当作offsetParent
二，如果该元素绝对／相对定位并且table没有绝对／相对定位，则会把body当作offsetParent
三，如果该元素绝对／相对定位并且table绝对／相对定位，则会把table当作offsetParent
看一下示例代码
1.<BODY >
<TABLE BORDER=1 ALIGN=right>
<TR>
<TD ID=oCell><div id="parentdiv" style="position:relative" >parentdiv<div id="sondiv">sondiv</div></div></TD>
</TR>
</TABLE>
</BODY>
运行结果:parentdiv.offsetParent.tagName IS "body"
sondiv.offsetParent.id IS "parentdiv"
2.<BODY >
<TABLE BORDER=1 ALIGN=right>
<TR>
<TD ID=oCell><div id="parentdiv" style="position:relative" >parentdiv<div id="sondiv" style="position:relative">sondiv</div></div></TD>
</TR>
</TABLE>
</BODY>
运行结果: parentdiv.offsetParent.tagName IS "body"
sondiv.offsetParent.id IS "parentdiv"
3.<BODY>
<TABLE BORDER=1 ALIGN=right>
<TR>
<TD ID=oCell><div id="parentdiv" >parentdiv<div id="sondiv" style="position:relative">sondiv</div></div></TD>
</TR>
</TABLE>
</BODY>
运行结果：parentdiv.offsetParent.tagName IS "TD"
sondiv.offsetParent.tagName IS "body"
4.<BODY >
<TABLE BORDER=1 ALIGN=right>
<TR>
<TD ID=oCell><div id="parentdiv" >parentdiv<div id="sondiv">sondiv</div></div></TD>
</TR>
</TABLE>
</BODY>
运行结果: parentdiv.offsetParent.tagName IS "TD"
sondiv.offsetParent.tagName IS "TD"
5.<BODY>
<TABLE BORDER=1 ALIGN=right style="position:relative">
<TR>
<TD ID=oCell><div id="parentdiv" style="position:relative" >parentdiv<div id="sondiv" style="position:relative">sondiv</div></div></TD>
</TR>
</TABLE>
</BODY>
运行结果: parentdiv.offsetParent.tagName IS "Table"
sondiv.offsetParent.tagName IS "parentdiv"
原文出处：http://villain564.javaeye.com/blog/370893