Abstract: In view of the problem that the disc spring clamping device of power head full hydraulic tunnel drill rig has small openings at present, it is impossible to add and unload the thick diameter drill tool in the middle, a large stroke compound nitrogen spring clamp is designed. Based on the analysis of the structure and working principle of the large-stroke compound nitrogen spring clamp, the clamping capacity and opening capacity of the clamping device are designed, and the maximum clamping force and minimum opening pressure are calculated. The test results show that the clamping device has large opening, reliable performance and meets the design and operation requirements.