把以下内容保存到网站根目录保存为web.config

<?xml version="1.0" encoding="UTF-8"?>
<configuration>
    <system.webServer>
        <security>
            <requestFiltering>
                <requestLimits maxAllowedContentLength="300000000" />
            </requestFiltering>
        </security>
    </system.webServer>
</configuration>