A power transmission system for a vehicle, comprising: an engine; a plurality of input shafts (11, 12), wherein at least one of the input shafts (11, 12) is configured to engage with the engine; each of the input shafts (11, 12) having a shift driving gear thereon; a plurality of output shafts (21, 22), wherein each of the output shafts has a shift driven gear configured to mesh with a corresponding shift driving gear; a motor power shaft, wherein the motor power shaft is configured to rotate together with one of the output shafts (21, 22); and a first motor generator configured to operate together with the motor power shaft; wherein when the motor power shaft is rotated together with the one of the output shafts, the first motor generator is configured to generate electric power utilizing at least parts of power generated by the engine while the vehicle is in a running state or a parking state, further comprising: a reverse output gear configured to selectively rotate together with a reverse idler gear configured to rotate together with a shift driving gear, characterized by further comprising a reverse synchronizer configured to selectively synchronize the reverse output gear with the reverse idler gear, wherein the reverse idler gear comprises: a first reverse idler gear configured to mesh with the shift driving gear; a second reverse idler gear configured to rotate together with the first reverse idler gear; a third reverse idler gear configured to mesh with the second reverse idler gear; wherein the reverse synchronizer is configured to selectively synchronize the reverse output gear with the third reverse idler gear, wherein the reverse output gear is coaxially arranged with the third reverse idler gear; wherein the reverse synchronizer is disposed on the reverse output gear to engage with the third reverse idler gear, wherein the reverse output gear and the third reverse output gear are fitted over the motor power shaft. an engine; a plurality of input shafts (11, 12), wherein at least one of the input shafts (11, 12) is configured to engage with the engine; each of the input shafts (11, 12) having a shift driving gear thereon; a plurality of output shafts (21, 22), wherein each of the output shafts has a shift driven gear configured to mesh with a corresponding shift driving gear; a motor power shaft, wherein the motor power shaft is configured to rotate together with one of the output shafts (21, 22); and a first motor generator configured to operate together with the motor power shaft; wherein when the motor power shaft is rotated together with the one of the output shafts, the first motor generator is configured to generate electric power utilizing at least parts of power generated by the engine while the vehicle is in a running state or a parking state, further comprising: a reverse output gear configured to selectively rotate together with a reverse idler gear configured to rotate together with a shift driving gear, characterized by further comprising a reverse synchronizer configured to selectively synchronize the reverse output gear with the reverse idler gear, wherein the reverse idler gear comprises: a first reverse idler gear configured to mesh with the shift driving gear; a second reverse idler gear configured to rotate together with the first reverse idler gear; a third reverse idler gear configured to mesh with the second reverse idler gear; wherein the reverse synchronizer is configured to selectively synchronize the reverse output gear with the third reverse idler gear, wherein the reverse output gear is coaxially arranged with the third reverse idler gear; wherein the reverse synchronizer is disposed on the reverse output gear to engage with the third reverse idler gear, wherein the reverse output gear and the third reverse output gear are fitted over the motor power shaft. a reverse output gear configured to selectively rotate together with a reverse idler gear configured to rotate together with a shift driving gear, characterized by further comprising a reverse synchronizer configured to selectively synchronize the reverse output gear with the reverse idler gear, wherein the reverse idler gear comprises: a first reverse idler gear configured to mesh with the shift driving gear; a second reverse idler gear configured to rotate together with the first reverse idler gear; a third reverse idler gear configured to mesh with the second reverse idler gear; wherein the reverse synchronizer is configured to selectively synchronize the reverse output gear with the third reverse idler gear, wherein the reverse output gear is coaxially arranged with the third reverse idler gear; wherein the reverse synchronizer is disposed on the reverse output gear to engage with the third reverse idler gear, wherein the reverse output gear and the third reverse output gear are fitted over the motor power shaft.