The invention discloses a piston with a variable lift compression ratio, aiming to solve the problems of complex mechanical structure, various parts and poor sealing performance of the prior art. The piston comprises an upper piston body part, an inner sleeve, a motor stator, a motor rotor, a motor base, a snap ring, a pressure spring and a lower piston body part, wherein the motor base is fixedly connected into an inner hole in the top end of the lower piston body part, and the motor stator is fixedly connected into a circular ring body at the center of the motor base; the bottom end surface of the motor stator is connected with the motor base in the circular ring body in a contacting manner, and the motor rotor is mounted in the center hole of the motor stator; the inner sleeve is mounted around the motor rotor and the motor stator in a sleeving manner, and a splined hole in the inner sleeve is matched with a spline shaft at the top end of the motor rotor; the pressure spring and the snap ring are mounted in the annular groove in the top end of the lower piston body part from bottom to top, and the upper piston body part is mounted at the top end of the lower piston body part; the upper piston body part is in threaded connection with the inner sleeve and connected with the lower piston body part in a sliding manner.