Plug-in four-wheel-drive hybrid vehicle and power transmission system thereof

The invention discloses a power transmission system of a four-wheel-drive hybrid vehicle. The power transmission system comprises a front drive system and a rear drive system. The front drive system comprises an engine, an electric generator, a front drive motor and a speed reducer, the front drive motor is in transmission connection with a front wheel differential in the speed reducer, the engine is connected with a front wheel speed reducer in the speed reducer, a clutch is arranged between coaxial gears connected with the engine and the front wheel differential in the speed reducer, and the engine is in transmission connection with the electric generator. On the premise of accomplishing the hybrid drive mode, the existing dual-clutch transmission is replaced by the gear reducer having the fixed transmission ratio, therefore the transmission structure is simplified, the speed reduce is small in size when being compared with the double-clutch transmission, and therefore the size of the power transmission system is decreased. The invention also discloses the four-wheel-drive hybrid vehicle comprising the power transmission system.