A driving assembly to be longitudinally placed in a vehicle, having a single power source, connected to a transmission shaft or a vehicle axle half shaft of the vehicle, provided with an automatic transmission, characterized in that: the automatic transmission comprises an input shaft, a power source is connected to the input shaft, an output shaft is provided coaxial with the input shaft, and an intermediate shaft is provided parallel to the input shaft; and a first-stage reduction-gear train is installed through the input shaft and the intermediate shaft, an Nth-stage reduction-gear train is installed through the intermediate shaft and the output shaft, N≥2, and each of the stages of the reduction-gear trains comprises a pair of gears having a different transmission ratio; characterized in that the output shaft of the power source and the input shaft of the automatic transmission are integrally manufactured, a rear cover of the power source and a front housing of the automatic transmission are integrated, and the driving assembly is placed in the front of the vehicle, and drives rear wheels of the vehicle; wherein longitudinally placed refers to that all of the axial direction of the output shaft of the power source and the axial directions of the input shaft, the intermediate shaft and the output shaft of the automatic transmission are in the direction of the length of the vehicle; wherein the first-stage reduction-gear train comprises an upper gear and a lower gear, the upper gear is fixedly connected to the input shaft of the automatic transmission via a key, the lower gear is fixedly connected to the intermediate shaft of the automatic transmission via a key, and a shifting clutch is provided between the upper gear and the input shaft of the automatic transmission; the shifting clutch is of an electromagnetically driving mode, and comprises a fixed fluted disc, a movable fluted disc and a power winding, the fixed fluted disc and the upper gear are integrated, the movable fluted disc is fixedly connected to the output shaft of the automatic transmission via a key, and when the power winding is electrified, the movable fluted disc moves axially along the output shaft of the automatic transmission to engage with the fixed fluted disc; the power winding is a sector-shaped winding, a semi-circular winding or a ring winding. the output shaft of the power source and the input shaft of the automatic transmission are integrally manufactured, a rear cover of the power source and a front housing of the automatic transmission are integrated, and the driving assembly is placed in the front of the vehicle, and drives rear wheels of the vehicle; wherein longitudinally placed refers to that all of the axial direction of the output shaft of the power source and the axial directions of the input shaft, the intermediate shaft and the output shaft of the automatic transmission are in the direction of the length of the vehicle; wherein the first-stage reduction-gear train comprises an upper gear and a lower gear, the upper gear is fixedly connected to the input shaft of the automatic transmission via a key, the lower gear is fixedly connected to the intermediate shaft of the automatic transmission via a key, and a shifting clutch is provided between the upper gear and the input shaft of the automatic transmission; the shifting clutch is of an electromagnetically driving mode, and comprises a fixed fluted disc, a movable fluted disc and a power winding, the fixed fluted disc and the upper gear are integrated, the movable fluted disc is fixedly connected to the output shaft of the automatic transmission via a key, and when the power winding is electrified, the movable fluted disc moves axially along the output shaft of the automatic transmission to engage with the fixed fluted disc; the power winding is a sector-shaped winding, a semi-circular winding or a ring winding.