The invention discloses a unidirectional damper which is mainly composed of a shell, a piston bolt, a washer cover, a spring washer, a piston sealing ring, a piston head, a piston rod, a T-shaped mounting seat, a through cover outer sealing ring, a through cover and a through cover inner sealing ring. A conic hole is formed in the piston head and is matched with a conic table at the end of the piston rod. When the movement direction and the conicity direction are the same, conic faces are matched to achieve a sealing function, and damping is small; and when the movement direction and the conicity direction are opposite, the conic faces are separated, and damping is almost zero. An oil groove is formed in the conic faces or the surface of the conic hole, or a round hole or a small gap is arranged on the piston head or the head of the piston rod, and unidirectional damping can meet the specific use requirement. Through self guide and good matching sealing performance of the conic faces,the function of unidirectional damping is achieved; and the structure is simple and reliable, the service life is long, the manufacturing difficulty is low, and economic benefits are high.