jquery:

$(function(){
$("#avg_day_live").bind("click",function(){   //点击

if($("#avg_day_live").attr("checked")=="checked"){ //现在的浏览器把 checked=true  改为了 checked="checked" (包含 disable)
$("#check_hour").attr("disabled","disabled");
}else{
$("#check_hour").removeAttr("disabled");
}

});

});

html:

<input type="checkbox" id="#avg_day_live" />

<select id="check_hour">

<option> one hour </option>

<option> twenty hour</option>

</select>