The invention discloses a buffer device of a hydraulic cylinder. The buffer device of the hydraulic cylinder comprises a piston (1), a cylinder barrel (2), a cushion collar (3), compression rings (4), screws (5), floating rings (6), a piston rod (7) and end covers (8). The end covers (8) are arranged at the two ends of the hydraulic cylinder, and the length of the portion, extending into a cylinder body, of each end cover exceeds a hydraulic fluid port. The piston (1) is fixed on the piston rod (7) and is sleeved in the cylinder barrel (2). The cushion collar (3) sleeved on the piston rod (7) is arranged on an adjacent side of the piston (1) and is in clearance fit with the piston rod (7). The compression rings (4) are fixed on inner end faces of the end covers (8) through the screws (5). The floating rings (6) are arranged between the compression rings (4) and the end covers (8) and are in clearance fit with the cushion collar (3). The buffer device of the hydraulic cylinder can improve buffer effect, and reduce machining difficulty and machining cost.