The present invention relates to prepaid services in the communication field. A method for charging a prepaid account includes: delivering the available traffic to the NAS based on the available balance of an account shared by the user and other users in response to a successful authentication of a user's access request; and delivering the available traffic to the NAS based on the available balance of the account shared by the user and other users in response to a receipt of an Accounting-Request-Interim message from the NAS. The solution provided by the invention may deliver the available traffic to a user every accounting period so that an account can be used by multiple users concurrently, whereas overdraft does not occur. The present invention also provides a system and an AAA server for charging a prepaid account.