The invention relates to a vertical splittable low-noise gearbox and a processing method thereof. The gearbox comprises a box body (1), a box cover (2) and three gear shafts (6); the box body (1) is of an integral structure, the box cover is fixed to one side of the box body, and a plurality of heat dissipation grooves (10) are formed in the outer surface of the other side of the box body and theouter surface of the box cover; the heat dissipation grooves (10) are distributed in the vertical direction; the gear shafts (6) are arranged in parallel in the vertical direction, and the two ends ofeach gear shaft (6) are supported on the box body and the box cover respectively, the middle gear shaft simultaneously meshes with the upper and lower gear shafts, and a plurality of oil guiding grooves (11) are formed in the inner wall of the other side of the box body and the joint surface of the box cover and run through an inner cavity of the box body and an inner cavity of the box cover. According to the vertical splittable low-noise gearbox and the processing method thereof, the technical problems that the center line of a power take-off shaft and the center line of a power generator are different and the rotation speed requirements of the power take-off shaft and the power generator are different are solved, and the gearbox meets the installation space requirement of equipment.