since im new to drupal7 and omega theme, I want a custom front page, so in drupal7 I create a page--front.tpl.php and everything's ok except the responsive design of omega theme, if I dont use page--front.tpl.php it works fine, I dont know how to create a custom page without screwing omega theme's RWD. thanks.
You can install the Delta Module which will allow you to create multiple versions of your theme settings page. Think of each version of your theme settings as a new "Template" or layout for your site, since layout is primarily controlled via the zones & regions configuration options of the Omega Theme settings.
Once you have created a new Delta template for your front page, you can apply it using the Context Module. Create a new Context for your Front Page. In this context, create a Condition first, choosing "Path" as the conditional operator and as the path itself. Then add a "Reaction", choosing "Delta" as the reaction, and select the "Front Page Template" you just created moments ago.