A method, performed by a user equipment (UE), is provided for uplink transmission. The UE determines transmission power of a sounding reference signal (SRS) toward a first cell belonging to a first timing advance group (TAG) and a physical uplink shared channel (PUSCH) toward a second cell belonging to a second TAG and whether to transmit both the PUSCH and the SRS, or drop the SRS. The UE transmits only the PUSCH but drops the SRS when the UE determines that the plurality of TAGs including the first and second TAGs are configured, that at least one symbol of a first subframe which is used to transmit the SRS toward the second cell of the second TAG is overlapped with a second subframe on which the PUSCH is transmitted toward the first cell of the first TAG and that a total uplink transmission power exceeds a maximum value.