知识点：使用 jq的prop才能设置
html
$('.ss').click(function(){
$(this).find("input[type=radio]").attr("checked",true);
});
<ul>
<li class="ss"><input type="radio" name="radio" class="fc" id="radio" value="a" />fdfd</li>
<li class="ss"><input type="radio" name="radio" class="fc" id="radio" value="b" />qqqq</li>
<li class="ss"><input type="radio" name="radio" class="fc" id="radio" value="c" />wwww</li>
</ul>
js
$('.ss').click(function(){
var $radio = $(this).find("input[type=radio]"),
$flag = $radio.is(":checked");
if( !$flag ){
$radio.prop("checked",true);
}
});