Abstract: The present application provides a pin shaft dismounting and mounting device, a frame body connecting structure and work machine. The pin shaft dismounting and mounting device for dismounting and mounting a pin shaft on a connecting seat, the pin shaft is provided with a through hole along the axial direction, and the device includes: a linear drive mechanism, including telescopic rods; and a pull rod configured to pass through the through hole, a first end of the pull rod being provided with an end cap structure, a connecting structure is disposed between a second end of the pull rod and an end portion of each telescopic rod. By the pin shaft dismounting and mounting device, a frame body connecting structure and work machine, the pin shaft may be dismounted and mounted conveniently and the problems of wear and deformation of the piston rod are solved.