The transmission is made up by reducer, out put gear shaft, eccentric bushing kits, packing ring kit sand some other parts. Gear reducer is directly driven by variable-frequency motor through force-limit coupling which passes the power further to spline shaft and output gear shaft. Eccentric bushing, sliding bearing and packing ring are assembled and connected to the furnace body together with flange and reducer. Center-to-center distance of the open-type gear transmission can be changed by adjusting the relative position of reducer and eccentric bushing to make up for deformation due to the high temperature.