Abstract: In order to resolve the problem of uneven water distribution, which was the main defect of UBF-SBR process in wastewater treatment used in a large-scale pig farm in Chongqing Hechuan, the operating characteristics of water distribution unit were studied with FLUENT software. Water distribution unit was one of the most critical units in UBF reactor. After simulation and optimization, a new water distribution unit was designed, which had a simple structure and was easy to be manufactured. Before the optimization, there were significant differences of velocities of flow among all outlets in water distribution unit. The maximum velocity was 4.1 faster than the minimum velocity. Through the optimization, however, the velocity differences were greatly reduced. The maximum velocity was only 0.6 faster than the minimum velocity. Practice has proved that the efficiency of wastewater treatment of UBF reactor has been enhanced obviously.