完整代码如下，将以下代码复制一下，保存一个web.config文件，放到网站根目录

<?xml version="1.0" encoding="UTF-8"?>
<configuration>
<system.webServer>
<rewrite>
<rules>
<rule name="sudu_rewritefunc_unifieddomainname" enabled="true" patternSyntax="ECMAScript" stopProcessing="false">
<match url="(.*)" ignoreCase="true" negate="false" />
<conditions logicalGrouping="MatchAll" trackAllCaptures="false">
<add input="{HTTP_HOST}" matchType="Pattern" pattern="^www\.baidu\.com$" ignoreCase="true" negate="true" />
</conditions>
<action type="Redirect" url="http://www.baidu.com/{R:0}" appendQueryString="true" redirectType="Permanent" />
</rule>

</rules>
</rewrite>
</system.webServer>

<system.webServer>
<defaultDocument>
<files>
<clear />
<add value="index.html" />
<add value="Default.htm" />
<add value="Default.asp" />
<add value="index.htm" />
<add value="iisstart.htm" />
<add value="index.asp" />
</files>
</defaultDocument>
</system.webServer>
</configuration>

效果是，不加www的域名跳转到加www的域名