A method performed by a first base station (3g-02) in a wireless communication system, the method comprising: transmitting (3g-25), to a second base station (3g-03), a first request message for adding the second base station for a terminal (3g-01); receiving (3g-35), from the second base station, a first response message for the first request message including configuration information on the second base station; transmitting (3g-40), to the terminal, a first message based on the configuration information on the second base station, the first message including first information for establishing a first split bearer associated with a first packet data convergence protocol, PDCP, entity for the first base station connected with both a first radio link control, RLC, entity for the first base station and a second RLC entity for the second base station, and second information for establishing a second PDCP entity for the second base station; transmitting (3g-85), to the second base station, a second request message for a handover of the terminal; receiving (3g-35), from the second base station, a second response message for the second request message; transmitting (3g-105), to the terminal, a second message for reconfiguring the first split bearer to a second split bearer, the second split bearer being associated with the second PDCP entity connected with both the first RLC entity and the second RLC entity; and releasing (3g-150, 3g-155) a connection between the first base station and the terminal, wherein the first split bearer is reconfigured to the second split bearer based on an establishment of the second split bearer and a release of a configuration for the first PDCP entity. transmitting (3g-25), to a second base station (3g-03), a first request message for adding the second base station for a terminal (3g-01); receiving (3g-35), from the second base station, a first response message for the first request message including configuration information on the second base station; transmitting (3g-40), to the terminal, a first message based on the configuration information on the second base station, the first message including first information for establishing a first split bearer associated with a first packet data convergence protocol, PDCP, entity for the first base station connected with both a first radio link control, RLC, entity for the first base station and a second RLC entity for the second base station, and second information for establishing a second PDCP entity for the second base station; transmitting (3g-85), to the second base station, a second request message for a handover of the terminal; receiving (3g-35), from the second base station, a second response message for the second request message; transmitting (3g-105), to the terminal, a second message for reconfiguring the first split bearer to a second split bearer, the second split bearer being associated with the second PDCP entity connected with both the first RLC entity and the second RLC entity; and releasing (3g-150, 3g-155) a connection between the first base station and the terminal, wherein the first split bearer is reconfigured to the second split bearer based on an establishment of the second split bearer and a release of a configuration for the first PDCP entity.