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