The invention provides a rotor engine capable of preventing air intake from returning flow. A cylinder body of the rotor engine is provided with an air inlet channel and an exhaust channel, a piston cylinder is arranged on the cylinder body, a rod cavity of the piston cylinder communicates with the air inlet channel, and a rodless cavity of the piston cylinder communicates with the exhaust channel; an air inlet is formed in a rod cavity of the piston cylinder, and an exhaust port is formed in a rodless cavity of the piston cylinder; and the reciprocating motion of the piston in the piston cylinder is used for accelerating the admission of mixed gas and discharging of waste gas. The rotor engine can effectively overcome the defects that in the process of air intake of the rotor engine; anddue to the fact that the pressure in the cylinder is too large, the mixed gas flows back, and thus the air inflow is reduced and the combustion is insufficient.