【index.html】编码：

<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>
</head>

<body>
    <iframe id="fr1" frameborder="1" style="width: 800;height:150px"></iframe>
    <p>
        <input type="text" name="userName" id="userName" placeholder="请输入姓名">
    </p>
    <p>
        <input type="text" name="info" id="info" placeholder="请输入信息">
    </p>
    <p>
        <input type="button" value="发送" onclick="sendMsg()">
    </p>
    <script>
        function sendMsg() {
            var userName = document.getElementById("userName").value;
            var info = document.getElementById("info").value;
            var url = "index.php?userName=" + userName + "&info=" + info;
            document.getElementById("fr1").src = url;
        }
    </script>
</body>

</html>

【index.php】编码:

<?php
$userName=$_GET['userName'];
$info=$_GET['info'];
var_dump($userName,$info);
?>

效果如下:

iframe_demo实例：消息发送(PHP版本)_pycharm