The embodiment of the invention discloses a data transmission method, a wap gateway and a data transmission system. The method provided by the embodiment of the invention comprises the steps as follows: the first wap gateway receives a terminal request message sent by a network element via a first MPLA VPN connection, and first Radius record information corresponding to the terminal request message is acquired by processing the terminal request message, and is synchronized to the second wap gateway which is mutually backup to the first wap gateway. In the method provided by the embodiment of the invention, on the one hand, the VPN connection can fully utilize network node bandwidth to reduce network congestion, so as to be more suitable for large flow processing; on the other hand, when disaster-tolerance switching is performing, operation is no longer related to network element equipment, the first gateway synchronizes the first Radius record information to the second gateway to achieve backup, so that when the first gateway is switched to the second gateway, the operation of forcibly making a user be offline and online again to register is not needed, and disaster-tolerance switching efficiency is greatly improved.