要使用jQuery删除所有CSS类，请使用removeClass()不带参数的方法。
您可以尝试运行以下代码来删除类：
<html>
<head>
<title>jQuery Example</title>
<script src = "https://cdn.staticfile.org/jquery/2.1.3/jquery.min.js"></script>
<script>
$(document).ready(function() {
$("p").removeClass();
});
</script>
<style>
.red {
color:red;
}
.green {
color:green;
}
</style>
</head>
<body>
<p class = "red" >This is first paragraph.</p>
<p class = "green">This is second paragraph.</p>
</body>
</html>