Brand-new hard gear surface big power change gear set possesses big torque scope and adapts unit structure modularization design and can be installed horizontally and vertically and has solid shaft output, hollow shaft output and contract disk hollow shaft output. Its applied scope is wide. It is made of high strength quality alloy steel through quenching and possesses high efficiency and long life gear and can bear large axial and radial load. It features low in run noise, high in reliability