The present invention discloses a method, system and terminal for accessing a Packet Data Serving Node. Said method comprises: directly accessing a service server to register through a WIFI module; receiving returned parameter information; carrying out PPP encapsulation for request information for establishing the PPP link to generate a first data packet; encapsulating said first data packet with one layer of TUNNEL header to generate a second data packet; encapsulating said second data packet with one layer of IP header based on a WIFI link to generate a third data packet and sending said third data packet to a WAG through a WIFI link; said third data packet being used for analyzing and dropping the IP header and TUNNEL header of said third data packet to recover the first data packet after being received by WAG, and recovered first data packet is analyzed by PDSN to establish a link connection.