A check valve is a device for preventing liquid from backflow in oil-gas-water collecting and conveying pipeline in oil enterprises and overcomes the defects in the prior art. The structural relationship of the check valve is as follows: a central through hole is arranged in a check valve body, and one end of the central through hole is a sealing surface which is sealed by a sealing ball; the sealing ball is fixed on a back-pressure valve slice which is connected on a valve mounting seat by a connecting shaft, and the valve mounting seat is fixed on the body; the other end of the check valve body is a mounting seat which is fixed in a pipeline; threads are arranged at the exterior of the check valve body, and a protective guard is connected with the check valve body by the threads; and a clamp is connected in the pipeline, so that the check valve body can be installed vertically and horizontally. When liquid flows into the check valve, the valve slice is propped open due to the pressure of the liquid, and the liquid flows through the pipeline; and after the liquid stops flowing, the valve slice returns to the valve body due to self gravity and liquid pressure at the rear section so as to play the role of sealing and intercepting the liquid, thereby preventing the backflow.