Most of the existing researches on the stress of the piston cups of drilling pumps neglect the fluid solid coupling between the piston liners and the drilling fluid during the working process of the drilling pump,and the conclusions drawn are different from the actual stress characteristics.In order to study the stress condition of the piston cup in the process of movement,the finite element model of the piston cylinder liner was established,and the mechanical characteristics of piston-liner were numerically simulated by fluid-structure coupling method.The effects of changing cup interference and lip angle size on the sealing performance of the piston-liner were discussed.The results show that the change rule of stress between the contact surface of the cylinder liner and the leather cup is similar to the change law of pressure inside the cylinder liner.Under the maximum working pressure,the equivalent stresses on the inner surface of the cylinder liner and the surface of the gasket in contact with the cup are relatively large,but compared to the cylinder liner and gasket,the cup is the most vulnerable part of the piston seal.The stress of the leather cup is mainly concentrated on the contact between the lip and root of the piston cup and the gasket,which are also two places where the leather cup is prone to failure.When the interference of the leather cup is greater than 1.0 mm and the lip angle is greater than 15°,the lip of the cup will produce a centripetal effect,which will affect the sealing performance of the cup.