A transmission device for a planetary gear train multi-gear hybrid vehicle and a transmission method therefore are provided. An input end of an input shaft is connected to an engine, an output end of the input shaft is connected to a front-end motor through a first planetary gear train, and the input shaft is connected to an output shaft through a first clutch. The output shaft is connected to a third planetary gear train, the third planetary gear train is connected to a second clutch and a second planetary gear train, and the second clutch and the second planetary gear train are both connected to a third clutch. The second planetary gear train is connected to a rear-end motor.