The invention provides a design method of the diameter of a technological hole of a large-sized thin-walled gear. The difference between the diameter of the technological hole of the gear and the diameter of a weight reducing concave ring of the gear is set to be 0.080-0.098. By the design method of the diameter of the technological hole of the large-sized thin-walled gear, provided by the invention, the distortion of the gear in the whole carburizing and quenching process can be reduced by more than 24%, the grinding amount of the gear is reduced, the manufacturing cost is greatly reduced, the uniformity of the tooth surface hardness is greatly improved, the quality of the gear is greatly improved, the bearing capacity of the gear is greatly improved, and the contact fatigue strength andthe bending fatigue are greatly improved.