Low speed and high torque water hydraulic motor is widely used in environmental protection and explosion-proof working conditions, such as coal mine, underwater action, military explosion-proof construction, etc. However, the low viscosity of water leads to serious wear and leakage of flow port pair in traditional motor with plate and shaft flow distribution. A type of water hydraulic motor with valve flow distribution structure was proposed and the piston flow distribution was realized by controlling onoff of valve through distribution cam. The kinematics of piston and motor output torque were theoretically calculated, and the corresponding relationship among push rod of flow distribution valve, valve core on-off and piston flow distribution states was revealed. The variation law of motor angular displacement fluctuation with angle and structure parameter K was analyzed. When structure design parameter K was 0.13, the fluctuation rate of motor torque was 6.59%. The simulation model of single piston with valve flow distribution was established in AMESim. Simulation results indicated that the maximum pressure drop of valve in flow distribution process was 0.08MPa. In single piston flow distribution, the valve port pressure responded quickly without high-pressure and low-pressure liquid connection. To verify the working performance of valve flow distribution in water hydraulic motor, a single piston with valve flow distribution test bench was established, and the working characteristics of valve under different working conditions were studied. The experimental results showed that the valve was stable under the working conditions of motor speed of 0~60r/min and pressure of 0~21.MPa. The pump outlet pressure fluctuated slightly when flow distribution state of piston chamber was switched, which had little effect on flow distribution process. The valve flow distribution structure can meet the flow distribution demand of crankshaft piston motor with swing cylinder. The relative sliding of the traditional motor flow port pair under water lubrication was converted into the valve on-off, which provided an idea for flow distribution of the water hydraulic motor with low speed and high torque.