Abstract: In this paper, the distribution of electric field of factory- composited DC insulators under different coating thicknesses and coating processes was simulated on the basis of finite element method for the constant electric field simulation. The distributions of electric field of the insulators including without RTV coating coated insulator, fully RTV coating coated insulator, partially RTV coating coated insulator and different RTV coating thickness insulator were obtained through simulation analysis. The calculated results show that the maximum electric field strength around the pin (coating edge) will not exceed the corona onset field strength in the air both for factory-composited porcelain and glass insulators when the RTV coating thickness is not less than 0.3 mm and the coat completely covers the surface of the insulator. While the electric field strength at the edge of the steel foot is very high when coating blank exists near the pin. The results in this paper provide guidance for optimizing the parameters of the anti-fouling flash coating of factory-composited insulators.