Abstract: RTV coating on the surface of the disc suspension insulators is an extremely effective anti-pollution flashover measure, which is widely used in all lines with different voltage levels of State Grid Corp., especially the UHVDC project. It effectively solves the problem of large-scale pollution flashover on transmission lines in our country, whereas raises new problems. The existing experience shows that the RTV anti-pollution flashover coating will affect the steep wave performance of the disc suspension porcelain or glass insulators to a certain extent. At present, there is less research on the extent of the RTV coating impact to insulators, as well as the steep wave characteristics of factory compound insulators as new products. This paper studied different tonnage products of disc porcelain and glass insulators for UHV project of State Grid Corp., conducted the air impact breakdown withstand voltage tests respectively in the Key Laboratory of State Grid Corp.. At the same time, the samples were modeled and analyzed the field intensity distribution through ANSYS simulation software. The test results show that the steep shock amplitude decreases to 2.4 p.u. for products with a mechanical strength of not more than 210 kN, and the amplitude decreases to 2.2 p.u. for that of not less than 300 kN. For the factory composite disc suspension insulators, it is suggested that corresponding steep wave impulse voltage amplitude criteria should be given according to different mechanical strength levels of the products.