The invention provides a lifting device for supporting a C-shaped or U-shaped arm of an X-
ray machine. The lifting device comprises an outer shell, an inner shell and a
gas spring arranged in the inner shell, wherein the inner shell is arranged inside the outer shell and can slide up and down inside the outer shell, and the C-shaped or U-shaped arm is connected to the inner shell; one end of the
gas spring is connected to the top of the inner shell, and the other end of the
gas spring penetrates through the bottom of the inner shell and is connected to the bottom of the outer shell; and the gas spring stretches and retracts to drive the inner shell to slide up and down. An
electromagnetic lock is arranged inside the inner shell, comprises a sliding sheet, and is used for locking or releasing the inner shell through the stretching and retracting of the sliding sheet. According to the invention, by means of the low-cost gas spring and the matched
electromagnetic lock and by utilizing the characteristic of the gas spring, the C-shaped or U-shaped arm can reach any position just by slightly pushing or pulling the inner shell, and thus, the operation of a doctor is facilitated; meanwhile, the gas spring can be used for effectively balancing the weight of the C-shaped or U-shaped arm, no noises are generated in a work process, so that the safety and the stability of the lifting of the C-shaped or U-shaped arm are effectively enhanced. The lifting device provided by the invention also has the advantages of simple structure and low cost.