The invention discloses an exhausting and supercharging coupling device for a lightweight aero-engine. Crankshaft supercharging impellers, a tail gas output box, a tail gas discharging impeller, a crankshaft and a rotating shaft are included; the crankshaft supercharging impellers are installed on the crankshaft due to key connection, and are arranged at the positions of the left side and the right side of a connection rod; the crankshaft supercharging impellers and the crankshaft are installed in a crankcase; the tail gas output box is arranged on one side of the crankcase, and is internallyprovided with the rotating shaft; and tail gas discharging blades are fixedly installed at the middle position of the rotating shaft. According to the exhausting and supercharging coupling device forthe lightweight aero-engine, due to amplifying on the crankshaft effect, on the premise that the lightweight aero-engine is not increased, the pressure of a gas exchanging port is increased by installing the crankshaft supercharging impellers and the tail gas discharging impeller, the external pressure of a gas outlet is lowered, the speed of air flowing through the interior of the engine is increased, and tail gas in a combustion chamber is discharged completely.