The utility model designs a lathe turning fixture for processing hydraulic cylinder piston sealing ring. The lathe turning fixture for processing hydraulic cylinder piston sealing ring comprises a fixture body which is characterized in that the fixture body is provided with an inner press plate and an outer press plate, and the outer press plate is provided with a splined groove, the inner press plate is provided with a splined shoulder, the splined groove and the splined shoulder are inserted into each other. The inner and outer press plates are specifically designed with a splined concave-convex groove structure, therefore the inner press plate and the outer press plate do not interfere with each other when processing thin-wall rings, and the end face compressing range can be maximized. The lathe turning fixture for processing hydraulic cylinder piston sealing ring has high universality, is applicable to computing and processing hydraulic cylinder piston sealing rings with similar structures and different dimensions, is able to machine the hydraulic cylinder piston sealing ring in a work compression state, thereby increasing the processing precision, meeting the requirement of bounce force of the sealing ring, and being applicable to processing thin-wall ring type parts and thin-wall ring type fan-shaped blocks.