A power transmission system for a vehicle, comprising: an engine unit configured to generate power; an input shaft, wherein the engine unit is configured to selectively engage with the input shaft when the engine unit transmits power to the input shaft; an output shaft configured to transfer at least partial of the power from the input shaft; an output unit configured to rotate differentially relative to the output shaft; a synchronizer disposed on the output shaft and configured to selectively engage with the output unit such that the output unit rotates synchronously with the output shaft, and the output unit is configured to output power to drive one or more front and /or rear wheels (210; 220) of the vehicle; a first motor generator configured to directly or indirectly couple with one of the input shaft and the output shaft for power transmission; and a second motor generator configured to drive one or more front or rear wheels (210; 220) of the vehicle; characterized in that: a plurality of the input shafts (21, 22) are provided, the plurality of input shafts (21, 22) are coaxial and fitted over one another sequentially, and the engine unit is adapted to selectively engage with one of the plurality of input shafts (21, 22) to transmit power to the one of the plurality of input shafts (21, 22); wherein one driving gear is fixed on each input shaft (21, 22), a plurality of driven gears are fixed on the output shaft, and the driven gears are meshed with the driving gears on the input shafts (21, 22) respectively, wherein the plurality of the input shafts comprises a first input shaft, a second input shaft fitted over the first input shaft, and a third input shaft fitted over the second input shaft. an engine unit configured to generate power; an input shaft, wherein the engine unit is configured to selectively engage with the input shaft when the engine unit transmits power to the input shaft; an output shaft configured to transfer at least partial of the power from the input shaft; an output unit configured to rotate differentially relative to the output shaft; a synchronizer disposed on the output shaft and configured to selectively engage with the output unit such that the output unit rotates synchronously with the output shaft, and the output unit is configured to output power to drive one or more front and /or rear wheels (210; 220) of the vehicle; a first motor generator configured to directly or indirectly couple with one of the input shaft and the output shaft for power transmission; and a second motor generator configured to drive one or more front or rear wheels (210; 220) of the vehicle; characterized in that: a plurality of the input shafts (21, 22) are provided, the plurality of input shafts (21, 22) are coaxial and fitted over one another sequentially, and the engine unit is adapted to selectively engage with one of the plurality of input shafts (21, 22) to transmit power to the one of the plurality of input shafts (21, 22); wherein one driving gear is fixed on each input shaft (21, 22), a plurality of driven gears are fixed on the output shaft, and the driven gears are meshed with the driving gears on the input shafts (21, 22) respectively, wherein the plurality of the input shafts comprises a first input shaft, a second input shaft fitted over the first input shaft, and a third input shaft fitted over the second input shaft. a plurality of the input shafts (21, 22) are provided, the plurality of input shafts (21, 22) are coaxial and fitted over one another sequentially, and the engine unit is adapted to selectively engage with one of the plurality of input shafts (21, 22) to transmit power to the one of the plurality of input shafts (21, 22); wherein one driving gear is fixed on each input shaft (21, 22), a plurality of driven gears are fixed on the output shaft, and the driven gears are meshed with the driving gears on the input shafts (21, 22) respectively, wherein the plurality of the input shafts comprises a first input shaft, a second input shaft fitted over the first input shaft, and a third input shaft fitted over the second input shaft.