According to one embodiment of the present invention, a method for reporting power headroom in a user equipment of a multi-carrier system, includes receiving a physical downlink control channel (PDCCH) signal comprising uplink resource allocation information from a base station; transmitting at least one of a physical uplink shared channel (PUSCH) signal and a physical uplink control channel (PUCCH) signal to the base station in a predetermined subframe based on the uplink resource allocation information in accordance with a transmission mode; calculating one or more power headroom values for the predetermined subframe in accordance with the transmission mode; and transmitting a report message comprising the one or more power headroom values to the base station, wherein the user equipment reports its first and second type power headroom values when operating in transmission mode A, or reports its first type power headroom value when operating in transmission mode B.