The helical gear is not exactly a helical gear, it should be said that the helical gear is the meshing mode of two helical gears, which is distinguished by the different directions in which they transmit the force in space. The common spur gear enters meshing along the tooth width at the same time, resulting in shock vibration noise and unstable transmission. Helical gear transmission is better than straight gear transmission, and the center distance can be tight for high-speed heavy load. Helical gear reducer is a novel reduction transmission device. Using the optimized and advanced design concept of module combination system, it has small size, light weight, large transmission torque, smooth starting, fine transmission ratio classification, and can be arbitrarily connected and a variety of installation positions can be selected according to user requirements.