<system.web>
     <httpRuntimeexecutionTimeout="36000"maxRequestLength="2097151"/>   <!--maxRequestLength：上传的大小，单位K   ,executionTimeout：设置超时时间，单位：秒。（默认是90秒） -->
</system.web>

注意：这个maxRequestLength最大值只能是2097151K,设置大于这个值将会出现如下错误:

Configuration Error

Description: An error occurred during the processing of a configuration file required to service this request. Please review the specific error details below and modify your configuration file appropriately.

Parser Error Message: The value for the property 'maxRequestLength' is not valid. The error is: The value must be inside the range 0-2097151.

Source Error:

3.  web.config下如果有如下节点(此节点是为IIS 7设计的) ，则修改
<requestLimitsmaxAllowedContentLength="2147483647" /> 单位与applicationhost.config中的<requestLimitsmaxAllowedContentLength="2147483647" />一致,它的最大值也只能为4294967295

<system.webServer>

<security>

<requestFiltering>

<requestLimitsmaxAllowedContentLength="2147483647" />

</requestFiltering>

</security>

</system.webServer>

总结：asp.net(IIS 7 and IIS 7.5)上传文件的最大值不能超过2GB