Provided is a transmission power control method for an uplink control channel of a terminal in a multi-carrier system where a plurality of downlink component carriers and at least one uplink component carrier are set in the terminal. The method includes: receiving a plurality of downlink grants from a base station; checking a Transmission Power Command (TPC) field included in each of the plurality of downlink grants; determining a transmission power of an uplink control channel (PUCCH) with a value of the checked TPC field; and transmitting the uplink control channel at the determined transmission power, with one configured uplink component carrier among the at least one uplink component carrier.