您将需要提供有关该问题的更多详细信息以及情况那么。您是在谈论在客户端停止此操作还是运行某些服务器端代码？什么开始下载首先和如何？这是你写的网站吗？您是否尝试控制单独的浏览器进程？ ... ...

how to stop automatic video downloading in iframe when a page become load

You're going to have to supply a lot more detail about the problem and the situation then that. Are you talking about stopping this on the client side or by running some server side code? What started this download in the first place and how?? Is this a site you wrote?? Are you trying to control a seperate browser process? ...??