A method of uplink power control in a wireless OFDMA system is provided. A serving base station first configures a fast feedback channel by transmitting a feedback allocation message to a mobile station. The mobile station then reports downlink channel information via the allocated fast feedback channel. Based on the reported downlink channel information, the serving base station estimates uplink channel quality and thereby detects a channel variation and generates an uplink power adjustment message that delivers a power offset to adjust the transmitting power level of the mobile station. In one novel aspect, the uplink power adjustment message also comprises feedback allocation information that re-configures the fast feedback channel without extra signaling overhead. In addition, the novel power adjustment message eliminates redundant information such that it is transmitted via a minimum resource unit without requiring extra resource.