Using propane as fuel, the HVAF thermal spraying technology of coating WC-12Co ceramic powder has low oxide content, less powder burn loss, and the wear resistance and corrosion resistance for ceramic powder can be maximized. Therefore, the technology has been widely applied in aerospace, petrochemical, national defense and other fields. A significant role is played by the air circulation cooling system in reducing thermal fatigue for gun body, extending service life and improving coating quality. It is of great significance to quantitatively reveal the effect mechanism in air circulation cooling conditions on the spraying process for improving the cooling effect and preparing high-quality coatings. At present, the numerical study on HVAF adopt 2D simplified model, the cooling cycle and cooling technical details for the gun system are not considered. In particular, the air flowing into the combustion chamber is simplified as mass flow rate, resulting in a deviation from the actual calculation. In this paper, a 3D numerical model for the whole gun including air cooling system, air/methane diverter and porous ceramic plate was established, the combustion reaction and flame flow characteristics were numerically solved. Based on the spray gun cooling system model and the simplified model were compared and analyzed, and relevant experimental analysis in the coating was carried out. The results show that it is necessary to consider the air-cooled circulation system in the modeling. A significant theoretical basis is provided by this model for preparing high-performance coatings and exploring the optimal cooling cycle effect.