The utility model discloses a pulley block speed multiplication mechanism for a hydraulic cylinder. The mechanism comprises a frame, a transmission rope I, a transmission rope II and a hydraulic cylinder I, wherein a fixed pulley I, a fixed pulley II, a fixed pulley III and a fixed pulley IV are connected with the frame in a rotatable way; a movable pulley assembly I is arranged between the fixed pulley III and the fixed pulley IV, and comprises a movable pulley I and a movable pulley II which are arranged in a sliding groove I of the frame; the movable pulley I is connected with the movable pulley II through a connecting piece I; one end of the transmission rope I is fixed on the movable pulley I and the other end of the transmission rope I is sequentially wound on the fixed pulley III, the movable pulley I and the fixed pulley I and is fixed on a workpiece; and one end of the transmission rope II is fixed on the movable pulley II and the other end of the transmission rope II is sequentially wound on the fixed pulley IV, the movable pulley II and the fixed pulley II and is fixed on the workpiece. The pulley block speed multiplication mechanism for the hydraulic cylinder can ensure that the motion of the workpiece is amplified to be more than 2 times that of the hydraulic cylinder, so that the problem that the motion stroke of a driving link is limited is solved.