采用onchange事件
<select id=select1 onchange="select1_onchange()">
<option value="aa">aa</option>
</select>
<input type=text id=text1><script language="javascript">
function select1_onchange(){
text1.value=select1.options(select1.selectindex).value;
}
</script>
<select id=select1 onchange="select1_onchange()">
<option value="aa">aa</option>
</select>
<input type=text id=text1><script language="javascript">
function select1_onchange(){
text1.value=select1.options(select1.selectindex).value;
}
</script>
<select id=select1 onchange="text1.value=this.value">
<option value="aa">aa</option>
<option value="bb">bb</option>
</select> <input type=text id=text1>
<Option Value="aa">aa</Option>
<Option Value="bb">bb</Option>
<Option Value="bb">bb</Option>
</Select>
<Input Name="T1">