The invention relates to a starter and generator integrated mechanism for an aircraft. The starter and generator integrated mechanism for the aircraft is designed for solving the problems that as an existing aircraft is provided with an electrical starting motor, a power generator and an engine, the occupied space is large, and weight is high. The starter and generator integrated mechanism for the aircraft comprises an engine and a starter. An overrun clutch A and an overrun clutch B are installed on a power output shaft of the engine. A first gear is installed on an output shaft of the starter. A second gear is arranged outside the overrun clutch A in a sleeving mode, and the first gear and the second gear are engaged. A first belt wheel is arranged outside the overrun clutch B in a sleeving mode, a second belt wheel is arranged outside the starter in a sleeving mode, and the first belt wheel and the second belt wheel are connected through a belt. The starter and a controller are connected through a wire, and the controller and a storage battery are connected through a wire. The starter and generator integrated mechanism for the aircraft has the advantages that the occupied space is small and weight is low.