The invention relates to a
tractor speed-changing box unit with
synchronizer commutation, comprising an
inverter unit, a main speed-changing unit and an auxiliary speed-changing unit which are arranged in sequence, wherein one end of the
inverter unit is connected with a
tractor engine, and one end of the auxiliary speed-changing unit is connected with a
tractor rear axle. By adopting the arranging manners, the tractor speed-changing box unit with
synchronizer commutation can transmit
motive power of the tractor engine to the tractor rear axle, a tractor front axle and a
power output shaft. By the combination of the
inverter unit, the main speed-changing unit and the auxiliary speed-changing unit, 12 forward gears and12 backward gears can be realized; the inverter unit is arranged at front end of the main speed-changing unit, which is convenient to realize commutation and gear engagement by adopting a
synchronizer structure and unnecessary to stop the tractor to engage gears in
low speed, therefore, the gear-shifting
impact and the gear-shifting force are small; the main speed-changing unit adopts a synchronizer to shift gears and is unnecessary to stop the tractor to shift gears, therefore, the gear-shifting
impact and the gear-shifting force are small; and an auxiliary speed-changing driven shaft and a bevel
pinion in the auxiliary speed-changing unit are integrated, therefore, the structure is compact.