There are provided an apparatus and method for transmitting information about power headroom in a multi-component carrier system. There is disclosed a method of configuring a plurality of component carriers combined from a candidate component carrier group, based on component carrier configuration information, triggering a power headroom report on the plurality of combined component carriers, calculating power headroom for the plurality of combined component carriers and transmitting combination power headroom information, including a value of the calculated power headroom, to a eNodeB. The power headroom report is triggered, when the power headroom on the plurality of combined component carriers is greater than or equal to a predefined threshold.Accordingly, uplink signaling overhead can be reduced because a power headroom report can be semi-persistently made without the need to additionally send information about the combination component carrier.