A power transmission system for a vehicle, comprising: an engine; a plurality of input shafts (11,12), at least one of the input shafts (11,12) being configured to selectively engage with the engine, each of the input shafts (11,12) being provided with a shift driving gear (1a-5a) thereon; a plurality of output shafts (21,22), each of the output shafts (21,22) being provided with a shift driven gear (1b-5b) configured to mesh with a corresponding shift driving gear (1a-5a); a motor power shaft configured to selectively rotate together with one of the input shafts (11,12); a first motor generator configured to rotate together with the motor power shaft, wherein when the motor power shaft rotates together with the one of the input shafts (11,12), the first motor generator uses at least a part of power output by the engine to generate electric power when the vehicle is parking or running, wherein the motor power shaft is configured to selectively rotate together with one of the output shafts (21, 22), wherein when the motor power shaft rotates together with one of the output shafts (21, 22), the first motor generator generates power and transmits the power to the one output shaft (21, 22); a motor synchronizer disposed on the motor power shaft, wherein the motor power shaft is configured to selectively rotate together with one of the input shafts (11,12) or one of the output shafts (21,22) via a synchronization of the motor synchronizer; a first motor gear; a second motor gear, the first motor gear and the second motor gear being freely fitted over the motor power shaft, wherein the first motor gear is configured to rotate together with one of the input shafts (11,12), the second motor gear is configured to rotate together with one of the output shafts (21,22), and the motor synchronizer is disposed between the first motor gear and the second motor gear, wherein the first motor gear is configured to perform a transmission with the shift driving gear (1a-5a) disposed on the one input shaft (11, 12); a middle idler configured to mesh with the first motor gear and the shift driving gear (1a-5a) provided on one of the input shafts (11,12) respectively; and characterized in that a reverse gear is freely fitted over the motor power shaft, wherein the reverse gear is configured as a duplex gear, the duplex gear comprising a first part meshed with a reverse idler gear and a second part meshed with a driven gear of a main reducer of the vehicle, the reverse idler gear is configured to mesh with the reverse gear and selectively rotate together with the middle idler, and a reverse synchronizer is configured to synchronize the middle idler and the reverse idler gear. an engine; a plurality of input shafts (11,12), at least one of the input shafts (11,12) being configured to selectively engage with the engine, each of the input shafts (11,12) being provided with a shift driving gear (1a-5a) thereon; a plurality of output shafts (21,22), each of the output shafts (21,22) being provided with a shift driven gear (1b-5b) configured to mesh with a corresponding shift driving gear (1a-5a); a motor power shaft configured to selectively rotate together with one of the input shafts (11,12); a first motor generator configured to rotate together with the motor power shaft, wherein when the motor power shaft rotates together with the one of the input shafts (11,12), the first motor generator uses at least a part of power output by the engine to generate electric power when the vehicle is parking or running, wherein the motor power shaft is configured to selectively rotate together with one of the output shafts (21, 22), wherein when the motor power shaft rotates together with one of the output shafts (21, 22), the first motor generator generates power and transmits the power to the one output shaft (21, 22); a motor synchronizer disposed on the motor power shaft, wherein the motor power shaft is configured to selectively rotate together with one of the input shafts (11,12) or one of the output shafts (21,22) via a synchronization of the motor synchronizer; a first motor gear; a second motor gear, the first motor gear and the second motor gear being freely fitted over the motor power shaft, wherein the first motor gear is configured to rotate together with one of the input shafts (11,12), the second motor gear is configured to rotate together with one of the output shafts (21,22), and the motor synchronizer is disposed between the first motor gear and the second motor gear, wherein the first motor gear is configured to perform a transmission with the shift driving gear (1a-5a) disposed on the one input shaft (11, 12); a middle idler configured to mesh with the first motor gear and the shift driving gear (1a-5a) provided on one of the input shafts (11,12) respectively; and characterized in that a reverse gear is freely fitted over the motor power shaft, wherein the reverse gear is configured as a duplex gear, the duplex gear comprising a first part meshed with a reverse idler gear and a second part meshed with a driven gear of a main reducer of the vehicle, the reverse idler gear is configured to mesh with the reverse gear and selectively rotate together with the middle idler, and a reverse synchronizer is configured to synchronize the middle idler and the reverse idler gear.