应该从内部工作functions.php

function add_manage_cat_to_author_role() 
{
    if ( ! current_user_can( \'author\' ) )
        return;

    // here you should check if the role already has_cap already and if so, abort/return;

    if ( current_user_can( \'author\' ) ) 
    {
        $GLOBALS[\'wp_roles\']->add_cap( \'author\',\'manage_categories\' );
    }
}
add_action( \'admin_init\', \'add_manage_cat_to_author_role\', 10, 0 );