A large gearbox supporting mechanism comprises a base and a supporting flat plate, a sliding way which is arranged in a front-and-back manner is arranged on the base, a sliding block is arranged at the bottom of the supporting flat plate, the sliding block is arranged in the sliding way in a sliding manner, the two sides of the front portion of the supporting flat plate are used for abutting against fixed supporting bases on the two sides of the head of a gearbox, two elastic supporting bases are arranged on the rear portion of the supporting flat plate in a spaced manner, a supporting portion abutting against the tail of the gearbox is arranged above the elastic supporting bases, an elastic supporting part is arranged between the supporting portion and each elastic supporting base, a vertical adjusting mechanism for driving the supporting portion to vertically move is arranged between the two elastic supporting bases, and a transverse adjusting mechanism for pushing the supporting flat plate to move left and right is arranged on one side of the supporting flat plate. The transverse adjusting mechanism is arranged and is used for left-and-right adjustment of the gearbox in the horizontal direction, it is ensured that the gearbox is placed fixedly and reliably, a vertical adjusting mechanism is arranged and is used for adjustment of the inclination angle in the vertical direction of the gearbox, and the gearbox is horizontal.