Abstract: The present invention provides an engine with variable compression ration comprising a cylinder cover, a cylinder body, a power output shaft and a crankshaft box, the cylinder cover is fixed on the cylinder body, the crankshaft box is formed with the cylinder body integrally; In the cylinder body, an piston is connected with a crankshaft via a connecting rod; the power output shaft is mounted on the crankshaft box; a power output gear is placed on the power output shaft, an input gear is placed on a crank journal of the crankshaft, the power output gear engages with the input gear; A supporting arm is placed in the crankshaft box, the crankshaft is hinged on the supporting arm; one end of the supporting arm is hinged on the crankshaft box, and the hinging shaft is the power output shaft; the other end of the supporting arm is a control end, the control end is connected with a rotation control mechanism, which can make the supporting arm rotate around the power output shaft.