The present invention relates to a system and method for achieving a Call Back service. The system includes a callback center and an online charging system (OCS) module. The method includes: the callback center receiving a callback request in which a calling party and a called party are both OCS subscribers, using a roaming number to call the calling party/called party, adjusting the charging duration of the firstly called party therein after the conversation is over, and then notifying the OCS module to deduct charges for both parties. The present invention is capable of charging reasonably and displaying the number accurately without any requirement on the cooperation of the pre-charge calling system, and the present invention is suitable to the intelligent network service which uses the OCS and the conventional intelligent network service.