A method for implementing a location update, the method is operated by a serving general packet radio service, GPRS, support node SGSN of a third generation, 3G, network system, the method characterized by comprising: receiving a first routing area update request message which contains at least a mixed location update indication and a routing area identification RAI, wherein said first routing area update request message is sent by a serving radio network subsystem SRNS of the 3G network system, wherein the first routing area update request message is generated after the SRNS adds the RAI to a second routing area update request message which contains at least the mixed location update indication, said second routing area update request message is received by the SRNS from a mobile terminal in the 3G network system, wherein the mixed location update indication indicates both a routing area update in the 3G network system and a location area update in a second generation, 2G, network system when the mobile terminal is camping on both the 2G network system and the 3G network system; obtaining the RAI from the first routing area update request message and performing, at least according to the RAI, a routing area update in the 3G network system; obtaining a location area identification LAI and an address of a visitor location register VLR which are of the 2G network system where the mobile terminal is located, at least according to the first routing area update request message; and sending a location area update request message, which contains at least the mixed location update indication and the LAI, to the VLR of the 2G network system corresponding to the address of the VLR, wherein the VLR implements a location area update in the 2G network system, at least according to the location area update request message. receiving a first routing area update request message which contains at least a mixed location update indication and a routing area identification RAI, wherein said first routing area update request message is sent by a serving radio network subsystem SRNS of the 3G network system, wherein the first routing area update request message is generated after the SRNS adds the RAI to a second routing area update request message which contains at least the mixed location update indication, said second routing area update request message is received by the SRNS from a mobile terminal in the 3G network system, wherein the mixed location update indication indicates both a routing area update in the 3G network system and a location area update in a second generation, 2G, network system when the mobile terminal is camping on both the 2G network system and the 3G network system; obtaining the RAI from the first routing area update request message and performing, at least according to the RAI, a routing area update in the 3G network system; obtaining a location area identification LAI and an address of a visitor location register VLR which are of the 2G network system where the mobile terminal is located, at least according to the first routing area update request message; and sending a location area update request message, which contains at least the mixed location update indication and the LAI, to the VLR of the 2G network system corresponding to the address of the VLR, wherein the VLR implements a location area update in the 2G network system, at least according to the location area update request message.