The present invention relates to a method for a terminal transreceiving data with a first base station supporting first radio access technology (RAT) and a second bases station supporting second RAT in a radio access system supporting Multi-RAT, and comprises the following steps: performing initial network entry with the first base station; negotiating with the first base station Multi-RAT capability for exchanging information necessary to access the second base station; performing the access process with the second base station; and simultaneously transreceiving data between the first base station and the second base station, which is accessed through the access process, wherein the step of negotiating Multi-RAT capability further comprises a step of transmitting control information that expresses a specific service flow or a QoS type, which prefers communication with the second base station, to the first base station.