需要配置两个地方：

1、

 <system.web>

<httpRuntime 

maxRequestLength="512000"

useFullyQualifiedRedirectUrl="true"

executionTimeout="6000"

minFreeThreads="8"

minLocalRequestFreeThreads="4"

appRequestQueueLimit="100"

enableVersionHeader="true" />

 </system.web>

2、

<system.webServer>

<security>

<requestFiltering>

<requestLimits maxAllowedContentLength="2147483647" />

</requestFiltering>

</security>

</system.webServer>