The present invention relates to a wireless communication system. More specifically, the present invention relates to triggering conditions for power headroom reporting (PHR) in a wireless network employing TDD scheme. According to one aspect of the present invention, the a user equipment (UE), receives information on a first time division duplex (TDD) uplink/downlink (UL/DL) subframe configuration, and information on a second TDD UL/DL subframe configuration informing the UE of a change from the first TDD UL/DL subframe configuration. And, the UE triggers a power headroom reporting (PHR), when the information on the second TDD UL/DL subframe configuration is received.