终于搞定了：
分享如下：在web.config里加两个地方：
<compilation debug="true">
.............
<buildProviders>
<add extension=".html" type="System.Web.Compilation.PageBuildProvider"/>
</buildProviders>
</compilation>
<httpHandlers>
...............
<add verb="*" path="*.html" type="System.Web.UI.PageHandlerFactory"/>
</httpHandlers>