The invention relates to the technical field of transmission systems, in particular to a hydraulic tensioner. The hydraulic tensioner comprises a shell, a plunger, a first elastic check ring and a second elastic check ring. The plunger is arranged in the shell and reciprocates along an inner cavity of the shell. A first limiting groove and a second limiting groove are formed in the side wall of the inner cavity of the shell. The first elastic check ring is arranged in the first limiting groove. The second elastic check ring is arranged in the second limiting groove. A third limiting groove and a fourth limiting groove are formed in the plunger. The third limiting groove is matched with the first elastic check ring. When the plunger and the shell move in the opposite directions to the maximum positions, the first elastic check ring enters the third limiting groove. The fourth limiting groove is matched with the second elastic check ring. When the plunger and the shell move away in the reverse directions to the maximum positions, the second elastic check ring enters the fourth limiting groove. According to the hydraulic tensioner, the plunger can only move between the third limiting groove and the fourth limiting groove, and the assembling difficulty of the hydraulic tensioner is lowered.