The utility model relates to a mechanics measuring device technical field especially is a spring dynamometer, including the casing, cup joint in the outside sleeve of casing and with sleeve matched with cover, the utility model discloses a sleeve of setting outside the casing and cover, after spring dynamometer finishes using, through set up on the sleeve outer wall the fixture block with set up the locking of working in coordination of draw -in groove on set cover inner wall, therefore, the sealing effect is realized, thereby avoided casing and inside metal parts to expose in the air, lead tosome parts to corrode, wearing and tearing, make the measuring error grow, the brief problem of life, the setting is at the limiting plate at casing top, the stopper of setting on the sleeve inner wall and reset spring between the two, spring dynamometer can make sleeve automatic re -setting when using, it fixes the sleeve to avoid the manpower, make things convenient for the survey measurements,promote teaching effects.