今天弄了半天，才知道jquery怎么去获取指定table的最后一行，所以就写了这2个函数，留着以后备用。
<script language="javascript" src="./jquery.js"></script>
<table border="1px #ooo" id="test" name="test" class="test" cellpadding="0" cellspacing="0" width="20%">
<tr id="1"><td width="30%">1</td><td width="30%">2</td><td width="30%">3</td></tr>
<tr id="2"><td width="30%">11</td><td width="30%">22</td><td width="30%">33</td></tr>
</table>
<table border="1px #ooo" id="test1" name="test1" cellpadding="0" cellspacing="0" width="20%">
<tr id="4"><td width="30%">1</td><td width="30%">2</td><td width="30%">3</td></tr>
</table>
<input type="button" name="button" value="add" onclick="addtr('test');">
<input type="button" name="button" value="del" onclick="deltr('test');">
<script>
//在id为test的table的最后增加一行
function addtr(id){
tr_id = $("#test>tbody>tr:last").attr("id");
tr_id++;
//alert(tr_id);
str = "<tr id = '"+tr_id+"'><td width='30%'>re1</td><td width='30%'>re2</td><td width='30%'>re3</td></tr>";
$('#'+id).append(str);
}
//删除id为test的table的最后一行
function deltr(id){
tr_id = $("#test>tbody>tr:last").attr("id");
$('#'+tr_id).remove();
}
</script>