Abstract: A mathematical model of the flow field in bilateral wedge-shaped crevice was built for ball piston pair. Based on the results obtained by cooperative solving the Reynolds equation and the energy equation, the pressure field and the temperature field were modified by each other. The viscosity field in ball piston pair was applied in calculating the characteristics of leakage, including the properties under different inlet pressure, speed and slip rate. The leakage caused by pressure drop and shear was differentiated. The simulation results show that the leakage increases with the inlet pressure, and the viscosity variety causes the raises of the leakage rate. The leakage caused by shear heating increases, but it is not significant under high pressure. The test results verify the simulation model.