A method for uplink transmission in a wireless communication system. A user equipment (UE) determines whether to transmit or drop a sounding reference signal (SRS) on a last symbol in a ith subframe. The SRS is dropped if multiple timing advance groups (TAGs) are configured, if a portion of the last symbol of the ith subframe for transmitting the SRS toward a first serving cell in a first TAG is overlapped with an (i+1)th subframe for transmitting an uplink channel toward a second serving cell in a second TAG and if a total power of the SRS and the uplink channel exceeds a maximum value on the overlapped portion of the last symbol.