Provided is a method for operating a transmission buffer in a wireless communication system. The method is performed by a user equipment (UE), and comprises detecting, in a switching layer, whether a transmission of data on a first transmission link is successful via the lower layer, determining whether to keep the transmission of the data on the first transmission link or to perform the transmission of the data on a second transmission link when the transmission of the data is not successful and performing the transmission of the data on the determined transmission link.