thanx Nilim for your reply,so I found a customized module for this feature named pos_transfer on Github and which only works with the updated point of sale module and not with the POS default module because of a problem on create_from_ui, but my question is why it's not working for me using odoo 9 is it something about this new version?

for all people interested in saving unpaid orders here is the link :

https://github.com/TheCloneMaster/point_of_sale.git 

it contains all uploaded POS related modules in addition of course to the pos_transfer and the updated point of sale moduleso I hope it works for you 

Hi Par Amina,

Currently by default in Odoo POS, it is not possible to save an order on POS Screen without making payment. We can invoice an order, but we cannot save an order without taking payment.

For this we need to have customized module wherein we can save an order.

Hope this helps

 Cheers!

you can use this module as entry point to achieve your goal 

https://apps.openerp.com/apps/modules/7.0/pos_backup_draft_orders/