Abstract: As the most advanced technological method for recovering total acid from stainless steel mixed acid waste, spraying and roasting can not only recover free acid and compound acid, but also recover metal oxide. In this process, the flow field and temperature field distribution chaos in the roaster will intensify metal oxide powder wall-hanging, and eventually lead to that the waste acid can not be fully reacted and corrode the roastor. In this study, simulation software Fluent was used to simulate the distribution of the flow field and temperature field in the roastor under different conditions such as air-fuel ratio and initial velocity of the post combustion gas, so as to obtain the optimal flow field and temperature field, eliminate the wall-hanging phenomenon of metal oxide powder to the maximum extent, and ensure the stable operation of the equipment for a long time. The results showed that the optimal flow field and temperature field distribution could be simulated when the gas medium was coal gas, the initial flow velocity of the post combustion gas was 20 m/s, and the air-fuel ratio was 1.7∶1. The actual measurement of the temperature gradient in the roaster under this optimal condition was basically consistent with the simulation results, which further verified the correctness of the model establishment. Under the condition of changing the gas medium to natural gas, the optimal flow field and temperature field distribution could also be simulated when the initial velocity of the post combustion gas was 20 m/s and the air-fuel ratio was 13∶1. The model could be used to guide the development, design and operation management of acid regeneration process in the future.