The process of zinc oxide production could be divided into two processes including fire and wet. French process is an important method for indirect ZnO production. A French ZnO furnace in Zhejiang Province is taken as the research object, the heating process and structure of the furnace are optimized and confirmed by means of numerical simulation and are tested through implementation, which effectively enhances thermal efficiency and extends the life-span of the furnace. By using numerical simulation of fire tunnel and combustion chamber, the effects of both burner type and furnace structure on the temperature field, flow field, and concentration field in the furnace are simulated and analyzed. Several reasonable optimization methods and reformation advices are put forward, and the simulation results are consistent with the field test results quite well. The furnace is reformed according to the simulation results, gas burner is changed from atmospheric to premixed, and the device for the air-fuel ratio adjustment is used to control the ratio of air and fuel, then the fire tunnel is changed from vertical structure to flaring structure. After these technique transformations as mentioned above, the gas consumption for one ton ZnO decreases from 240Nm³ to 192Nm³, and for each single day, 360Nm³ natural gas is saved, the average production of ZnO increases from 7.5t/d to 8.0t/d, and the life-span of the inner and outer crucibles of the furnace increases from three months to six months. The economy benefit due to the energy saving reconstruction is up to fifty thousand Yuan RMB per furnace per year.