Speed change gear with overrun clutching function

The invention provides a speed change gear with an overrun clutching function. The speed change gear comprises a speed change box, an output shaft, an overrun clutch, an input shaft and a transmission gear. The input shaft and the output shaft are connected with a starting motor and an engine respectively. The overrun clutch is installed on the input shaft through an inner ring and arranged in the speed change box. The transmission gear is fixedly installed on an overrun ring of the overrun clutch. By means of the speed change gear with the overrun clutching function, the overrun clutch, the input shaft and a driving gear are integrally designed, and the structure of the speed change gear is compact; meanwhile, the installation problem of the overrun clutch is solved, and the speed change gear is convenient to maintain, low in manufacturing cost, long in service life and high in reliability.