how to get total orders of a user? how can I get total price of all orders which owned by a single user? I want to assign different type of discounts by finding about total amount of their orders.
I'm using 


  hook_rules_action_info


.
should I use commerce_order_load_multiple() ?
Try this 

$orders = commerce_order_load_multiple(array(), array('uid' =&gt; $user_id));


You can use the conditions parameter of commerce_order_load_multiple.