The invention relates to a pneumatic cylinder and a dynamic end assembly using same for a direct-current converting switch. The pneumatic cylinder comprises a cylindrical cylinder body; a dynamic contact matching section, which sleeves the external circumferential surface of a corresponding part of a corresponding dynamic contact device, is arranged at the front part of the internal circumferential wall of the cylinder body; a dynamic contact seat matching section for guiding and assembling a corresponding dynamic contact seat is arranged at the rear part of the internal circumferential wall of the cylinder body, wherein the inside diameter of the dynamic contact matching section is more than that of the dynamic contact seat matching section; an opening expanding structure, which corresponds to an opening in the rear end of an air channel in a dynamic contact device, is arranged between the dynamic contact matching section and the dynamic contact seat matching section, wherein the opening expanding structure is that the inside diameter of the front is large, and the inside diameter of the back is small. According to the pneumatic cylinder and the dynamic end assembly using the pneumatic cylinder for the direct-current converting switch, air can be blown out smoothly through the opening expanding structure; the diameter of the dynamic contact matching section can be increased to improve the flowing capability; the diameter of the dynamic contact seat matching section can be reduced to reduce the contact area between the dynamic contact seat and the air in a pneumatic air chamber, and therefore, the pneumatic counterforce can be reduced, the load on an operating mechanism can be lowered down, the operation action is decreased, and as a result, the stability of the whole transmission system can be improved.