The invention discloses a plug-in type single-motor hybrid electric vehicle transmission which comprises a flywheel shock absorber, an engine connecting clutch, a planet gear set, a gear ring, a planet carrier, a sun gear and a planet row control clutch, wherein the gear ring, the planet carrier, the sun gear and the planet row control clutch are arranged in the planet gear set. The transmission further comprises a motor integrating a starting function, a drive function and a power generating function, a motor shaft connecting the motor with the sun gear, a brake controlling the gear ring to be fixed or rotate, a mechanical speed change system taking charge of transmission gear changes, an input shaft connecting the planet carrier with the mechanical speed change system, an output shaft connecting the mechanical speed change system with a main speed reducer, a battery system and a power distribution and electronic control system. The transmission has the beneficial effects that the structure of a single-motor system, a power synthetic system and the mechanical speed change system is adopted, the power performance is excellent, an engine and the motor work in the most economical rotation speed section, stepless speed regulation is matched with mechanical stepping gear shifting in the acceleration process, acceleration power is not interrupted, and the gear shifting efficiency and the gear shifting smoothness are extremely high.