The present invention relates to a wireless communication system. More specifically, the present invention relates to a method and a device for transmitting a power headroom reporting in the wireless communication system, the method comprising: generating a PHR MAC CE (Power Headroom Reporting MAC Control Element) for activated cells comprising a first cell and a second cell; and transmitting a power headroom reporting through the generated PHR MAC CE to a network in a subframe, wherein the generated PHR MAC CE includes a value of Type 2 PH (Power Headroom) information for the first cell followed by a value of a Type 2 PH information for the second cell, and the Type 2 PH information for the second cell followed by a value of Type 1 PH information for the first cell.