A transmission unit for a vehicle, comprising: a plurality of input shafts (11, 12), each of the input shafts 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; an output unit, wherein the output unit is configured to rotate with one of the output shafts (21, 22) at a different speed; an output synchronizer disposed on the one of the output shafts (21, 22) and configured to engage with the output unit to synchronize the output unit with the one of the output shafts; a reverse idler gear fitted over the one of the output shafts and configured to selectively engage with the output shaft; and a reverse output gear configured to mesh with the reverse idler gear, and further comprising a reverse synchronizer configured to synchronize the one of the output shafts with the reverse idler gear; wherein the reverse idler gear and the output unit share the output unit synchronizer; wherein the output unit synchronizer is configured as the reverse synchronizer, wherein the output unit comprises an output idler gear; wherein the output idler gear is fitted over the one of the output shafts (21, 22), further comprising a fixed output gear; wherein the fixed output gear is fixed on another one of the output shafts, and wherein the fixed output gear is meshed with a shift driven gear of a main reducer; wherein the output unit is meshed with the shift driven gear of the main reducer; wherein the reverse output gear is a joint gear structure; wherein one gear part of the joint gear is meshed with the reverse idler gear; and wherein the other gear part of the joint gear is meshed with the shift driven gear of the main reducer; further comprising: a generator gear fixed on one of the output shafts; a motor power shaft; and a motor power shaft gear fixed on the motor power shaft and configured to rotate together with the generator gear. a plurality of input shafts (11, 12), each of the input shafts 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; an output unit, wherein the output unit is configured to rotate with one of the output shafts (21, 22) at a different speed; an output synchronizer disposed on the one of the output shafts (21, 22) and configured to engage with the output unit to synchronize the output unit with the one of the output shafts; a reverse idler gear fitted over the one of the output shafts and configured to selectively engage with the output shaft; and a reverse output gear configured to mesh with the reverse idler gear, and further comprising a reverse synchronizer configured to synchronize the one of the output shafts with the reverse idler gear; wherein the reverse idler gear and the output unit share the output unit synchronizer; wherein the output unit synchronizer is configured as the reverse synchronizer, wherein the output unit comprises an output idler gear; wherein the output idler gear is fitted over the one of the output shafts (21, 22), further comprising a fixed output gear; wherein the fixed output gear is fixed on another one of the output shafts, and wherein the fixed output gear is meshed with a shift driven gear of a main reducer; wherein the output unit is meshed with the shift driven gear of the main reducer; wherein the reverse output gear is a joint gear structure; wherein one gear part of the joint gear is meshed with the reverse idler gear; and wherein the other gear part of the joint gear is meshed with the shift driven gear of the main reducer; further comprising: a generator gear fixed on one of the output shafts; a motor power shaft; and a motor power shaft gear fixed on the motor power shaft and configured to rotate together with the generator gear.