The life of the sealing ring affects the whole life of the hydraulic cylinder, and then affects the development of wave energy power generation in the form of hydraulic pressure energy convert. In this paper, a new kind of end seal and piston seal method was put forwarded based on the mechanism of annular gap lubrication and sealing. Considering the effects of shear stress on the near wall of the narrow gap, annular gap flow field mathematical model was established with goals of solving the leakage, power, and friction of gap sealing hydraulic cylinder. Results of experimental analysis and numerical solution show that the method of clearance seal could improve the working life and the efficiency of the hydraulic cylinder which working in high frequency.