The invention provides a two-stroke engine. The two-stroke engine comprises a cylinder body and a slider-crank mechanism; a compression chamber and a rotor cavity which communicate with each other arearranged in the cylinder body; a plurality of combustion chambers are formed by the wall surface of the rotor cavity and a rotor, a slider of the slider-crank mechanism moves in the compression chamber, and mixed gas in the combustion chambers is ignited so as to enable the rotor to rotate ; and an output shaft of the rotor is connected with a crank of the slider-crank mechanism through a transmission mechanism. The compression chamber communicates with the rotor cavity through a reducing pipe; and an air inlet channel is formed in the reducing pipe, and a one-way valve is arranged on the airinlet channel and is used for preventing backflow in a compression process. One end of the slider of the slider-crank mechanism is in a reducing shape, and the reducing end of the slider is matched with the reducing pipe and is used for compressing all the mixed gas in the compression chamber into the combustion chambers. According to the two-stroke engine, air inflow and air exhaust are completely separated, so that the scavenging process is omitted, and the charge loss caused by the fact that fresh mixed gas escapes from an exhaust port in the air inlet stroke is avoided.