The present invention relates to a method for transmitting an uplink (UL) data by a user equipment (UE) in a wireless communication system. In particular, the method includes the steps of: transmitting the UL data to a first node based on a first Quality of Service (QoS) flow to data radio bearer (DRB) mapping rule; receiving, from the first node, a handover command including information related to a second QoS flow to DRB mapping rule; transmitting the UL data to the first node based on the first QoS flow to DRB mapping rule, until an UL data path is switched from the first node to the second node; and transmitting the UL data to the second node based on the second QoS flow to DRB mapping rule, after the UL data path is switched from the first node to the second node.