The invention discloses a variable tappet, and belongs to the field of engine accessories. The variable tappet comprises a cylindrical upper rod piece and a cylindrical lower rod piece; the top of the lower rod piece is a continuous curve surface rising spirally along the axis of the lower rod piece, and a groove which rises spirally in the same way is formed in the curve surface; the bottom of the upper rod piece is arranged in the groove, and the axis of the upper rod piece is parallel to that of the lower rod piece all the time; an adjusting gear is connected to the bottom of the lower rod piece, the adjusting gear is meshed with a stripe-shaped rack, and the strip-shaped rack is perpendicular to the axis of the lower rod piece. The rising height range of the upper rod piece is obtained through conversion according to the relation of the combustion chamber height and the force arm length of a rocker arm, so that it is guaranteed that the upper rod piece makes contact with the rocker arm all the time, and operation of an air valve of an engine does not disturb operation of a piston. Accordingly, continuous controllable change of the tappet length can be achieved according to the actual demand so as to achieve intake and exhaust timing and continuous variable lifting, and research and improvement of engine full work condition dynamics and economy are promoted.