A disc hillside tractor with an efficient power speed-change system is provided. A main unit comprises a power source, a clutch, the efficient power speed-change system, a cab, a front profiled hinge block, a rear profiled hinge block, a main axle and a main unit travelling system; the auxiliary unit comprises an auxiliary axle, a frame, a lift, a steering arm and an auxiliary travelling system; the efficient power speed-change system comprises a high-power case, a combiner case and a transmission case connected in sequence; the high-power case comprises an input shaft, an incoming end gear pair, a power output shaft, a front gear pair, an outgoing end gear pair, and a front power shaft; the transmission case employs disc tractor speed-change structure; the combiner case comprises a power take-off gear, a coupling shaft, a planet gear set, a differential speed large gear, a front shaft, a rear shaft, an inter-axle differential, a bevel gear pair, a main axle differential, a main axle shaft, a static hydraulic transmission or a motor, and a motor gear; the disc hillside tractor has front and rear power interfaces, power stepless speed change, and chassis interchangeability, is simple to manufacture and is free of transmission part burnout.