后来发现，原来又是Apache没配置 好，是apache的mod_authz_host模块在起控制作用。
1.如果不启用vhosts
只需修改 httpd.conf
默认Directory节如下，注意红色部分，表示目录/usr/local/apache/htdocs允许所有 主机访问
<Directory "/usr/local/apache/htdocs">
#
# Possible values for the Options directive are "None", "All",
# or any combination of:
# Indexes Includes FollowSymLinks SymLinksifOwnerMatch ExecCGI MultiViews
#
# Note that "MultiViews" must be named *explicitly* --- "Options All"
# doesn't give it to you.
#
# The Options directive is both complicated and important. Please see
# http://httpd.apache.org/docs/2.2/mod/core.html#options
# for more information.
#
#Options Indexes FollowSymLinks
#
# AllowOverride controls what directives may be placed in .htaccess files.
# It can be "All", "None", or any combination of the keywords:
# Options FileInfo AuthConfig Limit
#
AllowOverride None
#
# Controls who can get stuff from this server.
#
Order allow,deny
Allow from all
</Directory>
由于主目录被指到别的地方了，所以将蓝色部分/usr/local/apache/htdocs换成你新的主目录就OK了。
2.启用vhosts
启 用vhosts的话，你就可以不作上面的修改了，因为VirtualHost可以单独配置这个节的属性，所以我们在VirtualHost这个节里配置的 话就更方便了，下面的配置中，我把我的网站放在/var/vhosts/www.test.cn下。
/usr/local/apache/conf/extra/httpd-vhosts.conf
<VirtualHost *:80>
<Directory "/var/vhosts/www.test.cn" >
#Deny from all
Allow from all
</Directory>
DocumentRoot "/var/vhosts/www.test.cn"
ServerName www.test.cn
</VirtualHost>
如果把Deny from all的注释去掉，那么服务器就会拒绝所有访问（和我们刚开始把主目录移动到htdocs外而没做任何配置修改时一样，哈哈）
补充一点：
如果你是写个index.php放在目录下测试，可要注意了，记得加上默认主页index.php
DirectoryIndex index.html index.php