The influences of ultrasonic field to polishing performance of Polishing Based on Coupling Vibration of Liquid (PCVL) are analyzed here. The simulation results shows that sound field in the original polishing device is rather uneven due to the existence of standing wave. To obtain better polishing performance, the experimental equipment was modified. Uniformity of the sound field was improved by preventing standing wave, thus a better surface quality could be achieved. Furthermore, a higher machining efficiency could be also obtained because sound intensity was strengthened at the same time. From the results serials of experiments, the improvements made by modified equipment are clearly shown.