A traffic mobility method between heterogeneous access networks of a wireless communication system includes, as a user equipment (UE) multiply accesses a first access network and a second access network, configuring a first transmission path corresponding to the first access network and a second transmission path corresponding to the second access network with respect to the UE, by a gateway, determining whether traffic mobility is performed on each traffic flow based on a traffic mobility policy of the each traffic flow served to the UE through the first transmission path and a transmission state of the second access network, by a control entity, and changing a transmission path of a traffic flow on which traffic mobility is determined, to the second transmission path from the first transmission path, by the gateway.