@masoud2011
in prestashop 1.6 you can achieve it as follows: 1- Check the css class of the new tab you made (it should be like this "icon-AdminMyModule" assuming your admin controller for the tab name is "AdminMyModuleController". 2- Create a css file in your module "menuTabIcon.css" and add the code you need, for example:
.icon-AdminMyModule:before{
content: "\f021";
}
3- register your module with the "displayBackOfficeHeader" hook and implement this method:
public function hookDisplayBackOfficeHeader($params) {
$this->context->controller->addCSS(($this->_path) . 'menuTabIcon.css');
}
You're done, this will display a refresh icon behind the menu item, if you need codes for other icons, find them here in the Fontawesome cheat sheet