<system.web>

  <httpRuntime requestValidationMode="2.0" maxRequestLength="" ></httpRuntime>

  <!--单位：KB =3MB   默认是4MB,最大支持2GB-->

 </system.web>

<system.webServer>

 <security>

      <requestFiltering>

        <requestLimits maxAllowedContentLength="" />

        <!--单位：字节B  = GB 默认是4MB,最大支持2GB-->

      </requestFiltering>

    </security>

</system.webServer>