RewriteEngine On
RewriteCond %{HTTP_HOST} ^(www.)?xxx.com$
RewriteCond %{REQUEST_URI} !^/blog/
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule ^(.*)$ /blog/$1

没有输入文件名的默认到到首页

RewriteCond %{HTTP_HOST} ^(www.)?xxx.com$
RewriteRule ^(/)?$ blog/index.php [L]

.htaccess中的apache rewrite规则详解

原文：http://blog.51cto.com/xiaogongju/2060949