Provided is a large-torque synchronizer. The large-torque synchronizer comprises a gear hub which is sleeved with a gear sleeve. The two sides of the gear hub are each provided with a shifting gear. The outer wall of the inner end of each of the two shifting gears is provided with a combination gear ring. Each of the two combination gear rings is sleeved with a locking gear ring. Each of the two locking gear rings is sleeved with a synchronous ring. The outer conical face of each synchronous ring and the inner conical face of the corresponding gear sleeve are matched. Spline teeth are arranged on the inner surface of each synchronous ring in the peripheral direction. Each spline tooth is provided with a tooth side face and a locking face. The outer surface of each locking gear ring is provided with a spline tooth groove matched with the spline teeth of the corresponding synchronous ring. A spline tooth groove limiting face and a spline tooth groove locking face are sequentially arranged on the side face of the inner end of each spline tooth groove from inside to outside. A convex plate is arranged on the outer surface of each locking gear ring. The top face of each convex plate is provided with a convex plate arc face and a convex plate transitional slope. Each convex plate arc face and the outer surface of the corresponding locking gear ring are arranged coaxially. A reset groove is formed in the position, corresponding to an elastic pressing ring, of each inner conical face and can drive the elastic pressing ring to reset. The large-torque synchronizer is suitable for gearboxes.