<input type="button" value="获取验证码"> 

 input[type=button]
  width: 150px;
  height: 30px;
  background-color: #ff3000;
  border: 0;
  border-radius: 15px;
  color: #fff;
 }
 input[type=button].on {
  background-color: #eee;
  color: #ccc;
  cursor: not-allowed;
 }

 $("input[type='button']").click(btnCheck);
  /**
  * [btnCheck 按钮倒计时常用于获取手机短信验证码]
  */
  function btnCheck() {
   $(this).addClass("on");
   var time = 5;
   $(this).attr("disabled", true);
   var timer = setInterval(function() {
    if (time == 0) {
     clearInterval(timer);
     $("input").attr("disabled", false);
     $("input").val("获取验证码");
     $("input").removeClass("on");
    } else {
     $('input').val(time + "秒");
     time--;
    }
   }, 1000);
  }