The invention relates to a pressure control valve, in particular to a back pressure valve. The back pressure valve solves the problems that a piston of an existing back pressure valve deviates easily,carbon deposition enters a lining easily to block motion, back pressure mismatch is caused, and maintenance is frequent. According to the scheme, the back pressure valve comprises a back pressure valve body, a pipe-like lining is arranged in the back pressure valve body, a sealing base is arranged between the left end of the lining and the valve body, an O-shaped ring is arranged between the sealing base and the valve body, the end head of a piston is larger than the inner diameter of the lining, a weight reducing groove is formed in the side face, the extending-in length is larger than the extending-out length, and two O-shaped rings are arranged on the matching face with the lining. The back pressure valve has the beneficial effects that 1, the O-shaped ring is arranged between the sealing base and the valve body, sealing performance is better, and maintaining is convenient; 2, F4 rings on the piston are replaced by the O-shaped rings, the compression amount is optimized, the position of a sealing groove is improved, the sealing effect is better, waste gas and waste water can be extruded out, and forming of carbon deposition is avoided; 3, the piston is reasonable in shape and structure, and is prevented from deviating from the center line; 4, the head portion of the piston blocks the lining; and 5, the piston slides stably and smoothly, and the maintenance frequency is low.