The utility model provides a gearbox, include power input shaft, middle output shaft, the speed change mechanism that shifts, control the semi -axis, the speed change mechanism transmission of shifting is connected between power input shaft and middle output shaft, installs drive wheel and output gear on the left and right sides semi -axis, be provided with a set of biography dynamic wheel group between middle output shaft and the left and right sides semi -axis respectively, middle output shaft makes drive wheel corotation or reversal through two power transmission path that pass dynamic wheel group. Passing power transmission path of dynamic wheel group and making drive wheel corotation, another makes the drive wheel reversal, apply the brake one of them half epaxial drive wheel, second half epaxial drive wheel corotation realizes turning, one of them half epaxial drive wheel reversal, second half epaxial drive wheel corotation realizes the pivot turn. The rotate on site that is just reversing is difficult to sink, when unilateral braking rotate on site has resulted in the track to sink, use the rotate on site mode can remove the sagging predicament of track. Can adapt to the less environment in landmass.