A method, apparatus, and system for efficiently reporting Power Headroom (PH) for optimizing uplink coverage are provided. A method in which user equipment reports power headroom in a mobile communication system includes receiving Power Headroom Report (PHR) configuration information including a PH threshold value from a first base station, determining whether to perform a PHR trigger by comparing the PH value, which indicates the available transmission power of the user equipment, with the PH threshold value, and, when the PH value is less than the PH threshold value, transmitting, to the first base station, PHR-related report information including information corresponding to an influence caused by the scheduling of the first base station.