http://localhost/theme/category.php?name=bush
http://localhost/theme/category/bush

this is my rewrite rule
#RewriteRule ^test/([a-zA-Z0-9]+)$ test.php?name=$1 [L]

I add echo $_GET['name'] to test my category.php page, no value showed. did I do something wrong?

From your example url, you should use such rules:

RewriteRule ^category/([a-zA-Z0-9]+)$ category.php?name=$1 [L]

And place the .htaccess to the theme directory.