A hybrid-power driving system, in which six forward speed ratios are available by switching only three synchronizers (7, 26, 9), comprising: an input shaft carrying a first driving gearwheel, a second driving gearwheel, a third driving gearwheel, and a fourth driving gearwheel disposed thereon; a first synchronizer, disposed on the input shaft, for releasably synchronizing at least one of the first driving gearwheel and the second driving gearwheel to the input shaft, a second synchronizer, disposed on the input shaft, for releasably synchronizing at least one of the third driving gearwheel and the fourth driving gearwheel to the input shaft; an output shaft carrying a speed-reducing gearwheel, a first driven gearwheel, a second driven gearwheel, and a third driven gearwheel disposed thereon; a first intermediate shaft carrying a fourth driven gearwheel and a fifth driven gearwheel disposed thereon, wherein the first intermediate shaft includes a hollow portion and is coaxial to the output shaft; a third synchronizer, disposed on the output shaft, for releasably synchronizing at least one of the first driven gearwheel and both the fourth driven gearwheel and the fifth driven gearwheel to the output shaft; a second intermediate shaft carrying a sixth driven gearwheel, a seventh driven gearwheel, an eighth driven gearwheel, and a ninth driven gearwheel disposed thereon; a motor shaft carrying a fifth driving gearwheel disposed thereon; a final driven gearwheel; a sixth driving gearwheel carried by the input shaft, wherein the ninth driven gearwheel is slidable to releasably mesh with the sixth driving gearwheel; and wherein the sixth driving gearwheel is disposed on the second synchronizer. an input shaft carrying a first driving gearwheel, a second driving gearwheel, a third driving gearwheel, and a fourth driving gearwheel disposed thereon; a first synchronizer, disposed on the input shaft, for releasably synchronizing at least one of the first driving gearwheel and the second driving gearwheel to the input shaft, a second synchronizer, disposed on the input shaft, for releasably synchronizing at least one of the third driving gearwheel and the fourth driving gearwheel to the input shaft; an output shaft carrying a speed-reducing gearwheel, a first driven gearwheel, a second driven gearwheel, and a third driven gearwheel disposed thereon; a first intermediate shaft carrying a fourth driven gearwheel and a fifth driven gearwheel disposed thereon, wherein the first intermediate shaft includes a hollow portion and is coaxial to the output shaft; a third synchronizer, disposed on the output shaft, for releasably synchronizing at least one of the first driven gearwheel and both the fourth driven gearwheel and the fifth driven gearwheel to the output shaft; a second intermediate shaft carrying a sixth driven gearwheel, a seventh driven gearwheel, an eighth driven gearwheel, and a ninth driven gearwheel disposed thereon; a motor shaft carrying a fifth driving gearwheel disposed thereon; a final driven gearwheel; a sixth driving gearwheel carried by the input shaft, wherein the ninth driven gearwheel is slidable to releasably mesh with the sixth driving gearwheel; and wherein the sixth driving gearwheel is disposed on the second synchronizer.