var sex  = $("#search_form select[name='sex'] option:selected ").attr("value");


	var sex = $("#search_form select[name=sex'] option[selected]").attr("value");
这样写会有问题 sex的值有时是undifined 
改为
var sex  = $("#search_form select[name='sex'] option:selected ").attr("value");

	var val = $("#search_form select[name='sex']").children('option:selected').val();
这样就去到了