The invention discloses a two-gear fixed-shaft type gearbox. The two-gear fixed-shaft type gearbox comprises a shell body, an input shaft, an idler shaft, a transmission shaft and an output shaft, wherein the input shaft, the idler shaft, the transmission shaft and the output shaft are arranged in the shell body from top to bottom in sequence and are connected with the shell body correspondingly; the input shaft is provided with an input flange, a first second-gear driving gear, a first clutch, a second clutch, a first first-gear driving gear and a transition driving gear in sequence from left to right, the idler shaft is provided with a second second-gear driving gear, a third clutch, a fourth clutch, a second first-gear driving gear and a transition driven gear in sequence from left to right, the transmission shaft is sleeved with a second-gear driven gear, a three-axis driving gear and a first-gear driven gear in sequence from left to right, and the output shaft is sleeved with a left output flange, an output gear and a right output flange in sequence from left to right. By means of the two-gear fixed-shaft type gearbox, different requirements for low-speed and medium-speed operation of a traction engine can be met; and meanwhile, the defects that a large-power gearbox in an existing traction engine only has one gear and is heavy, high in cost, long in reversing or gear-shifting time, low in efficiency and the like are overcome.