The novel relates to the field of air compressing, in particular to a novel compression air cylinder for a hydraulic-drive piston compressor. The novel compressing air cylinder comprises an air cylinder body and a piston; the air cylinder body comprises an upper end cover, a lower end cover and a middle cylinder body; the middle cylinder body is a cylindrical middle cylinder body; a piston cavity is formed by the lower end face of the upper end cover, the upper end face of the lower end cover and the inner wall of the middle cylinder body; the lower end face of the upper end cover and the upper end face of the lower end cover are each provided with a round groove; conical faces are arranged on the edges of the round grooves; conical faces are arranged on the edges of two end faces of the piston head; and according to the novel compression air cylinder, the centering degree of the working stroke of the piston in the compression air cylinder can be improved, eccentric wear of a piston sealing piece is reduced, the service life of a part is prolonged, and the centripetal action force on the conical faces through fluid pressure is used for improving the centering effect of the axis of the piston body and the axis of the air cylinder.