function rsces(){
var input=document.getElementsByTagName("input")
var qwq;
for (qwq=0;qwq<input.length;qwq++){
input[qwq].value=" "
}
}
<html>
<head>
<title>肯德基点餐系统</title>
</head>
<body>
<h1>肯德基点餐系统</h1>
<h2>汉宝宝：￥10</h2>
<input type="number" id="one">
<h2>数条：￥5</h2>
<input type="number" id="two">
<h2>渴了：￥2</h2>
<input type="number" id="three"><br/><br/>
<button onclick="sumbie()">踢脚</button>
<button onclick="rsces()">晴空</button>
<h2>总计：</h2>
<input type="number" id="four">