The invention discloses a rotor engine capable of doing reciprocating arc motion with a variable compression ratio, and belongs to the field of mechanical-electrical integration. The rotor engine comprises wet type clutches, an angular displacement sensor, a transmission gear, a reversing shaft and the like, and is characterized in that the angular displacement sensor can continuously detect a rotation angle of a rotor relative to a position B; when judging that the angle reaches an angle set by a system, a vehicle-mounted ECU controls a hydraulic system to be connected into or disconnected from each wet type clutch to switch a transmission line, so that the reciprocating arc motion of the rotor can be converted into unidirectional circumferential motion of an output shaft; meanwhile, the vehicle-mounted ECU can judge whether to change the compression ratio of the engine according to a running condition of a vehicle; when the compression ratio is needed to be changed, the vehicle-mounted ECU changes the maximum angle value, which is set by the system at the present, of rotation of the rotor according to a preset factory model of the vehicle, so that the maximum angles of rotation of the rotor of the engine are different, and the total volume of a cylinder is changed, but the volume of a combustion chamber is unchanged; and therefore, the compression ratio is changeable. The rotor engine has the advantage that the compression ratio of the rotor engine is changeable; and moreover, the compression ratio range is relatively wide, and the maximum compression ratio is relatively large.