A new kind of valve plate is designed, which is suitable to use on cylinder fixed and valve plate rotating of water hydraulic piston motor. By using computational fluid dynamics software FLUENT, the motors threedimensional model of its working process was established, and the transient stimulation and calculation were done by using sliding mesh and dynamic mesh technology, then its flow characteristics of the valve plate were studied. It was shown that the pressure drop (rebound) and rise (down) phenomenon of the piston chamber disappeared during its high and low pressure switching in the cavity of piston while the symmetrical valve plate had a Ushaped groove at both end of the waistslot. Thus, the phenomenon of water hammering and erosion of cavitation caused by pressure mutation were avoided. Besides, the flow curve crests shock phenomenon is obviously disappeared, and the piston motor works more steady, which provides a reference for the improved design of water hydraulic motors valve plate.