The utility model relates to a check valve, in particular to a piston type water impact preventing and high-pressure balancing check valve, which comprises a valve body and a valve flap. The valve body is provided with an inlet channel, an outlet channel and an accommodating cavity used for accommodating the valve flap, the valve flap can slide in the accommodating cavity, the rear end of the accommodating cavity is provided with a valve cover, the valve body is also provided with a valve seat matched with the front end of the valve flap in a sealing way, the valve flap divides the accommodating cavity into a front chamber and a rear chamber, the rear chamber is a closed chamber, a bypass pipeline is arranged outside the valve body, and the two ends of the bypass pipeline are respectively connected with the rear chamber and the outlet channel. When a medium returns, the valve flap rapidly slides down to close under the gravity and the impact of the returning medium, the volume of the rear chamber is increased instantly after the valve flap slides down, high negative pressure can be generated when the medium is not supplemented promptly, the valve flap can close slowly under traction of the negative pressure, the pipeline damage caused by 'water impact' during rapid closing of the check valve is effectively avoided, and the service life of the check valve is prolonged.