The present invention relates to a method for maintaining continuity of Diameter online charging. The method comprises the following steps: a) initializing, when a user is moving, the relocation of a prepayment client terminal from an old prepayment client terminal to a new prepayment client terminal, and implementing the re-authentication of a mobile station at the new prepayment client terminal; b) transmitting the context information of an old Diameter online charging session from the old prepayment client terminal to the new prepayment client terminal after the re-authentication has been successfully completed; c) transmitting an initial credit control request (CCR) message comprising the identification of the old Diameter online charging session from the new prepayment client terminal to a prepayment server for continuing the old Diameter online charging session, and request for a quota by a prepayment proxy to the prepayment server via the new prepayment client terminal; and d) disconnecting the old connection between the old prepayment client terminal and the prepayment server.