Abstract: An analysis of the large-scale hydraulic hoist cylinder piston is carried out, in which geometric distortion caused by the joint gap of the hydraulic cylinder and the effect of rod axis lateral deformation for the gravity of the hydraulic cylinder piston have been considered. A quantitative calculation for load-deformation of the hydraulic cylinder piston is presented according to the basic principle of solid mechanics. Moreover a practical calculation example is given. In this paper, some misunderstanding is pointed out on the security control condition for the piston. The results show that it is the ultimate load coefficient problem to consider the effect of geometric distortion and gravity. Its security is controlled by the strength. The results would be helpful in the design layout for the hydraulic hoist cylinder piston in the large-scale gate of surface discharge outlet and guide the safe opera-tion of the existing hydraulic hoist cylinder pistons in the hydropower project.