The epoxy composite coating composited by zinc rich epoxy primer, waterborne polyurethane intermediate coating and silver epoxy enamel was sprayed on the surface of Q235 steel. The anticorrosion of as-prepared samples in substation environment with atmospheric exposure for 18 months, and in 5% NaCl aqueous solution for 250 days were evaluated and compared, respectively. Electrochemical impedance spectroscopy(EIS) was employed to analyze the corrosive behavior of epoxy composite coating in 5% NaCl aqueous solution, the weather and the salt resistance were also evaluated. Additionally, the structure changes of the epoxy composite coating induced by salt immersion and atmospheric exposure were characterized by Fourier transform infrared(FT-IR). The results are demonstrated that the epoxy composite coating is corroded to be invalid after immersed into 5% NaCl aqueous solution for 250 days, and the impedance decreases from 3.967×10⁹ Ω·cm² to 9.780×10² Ω·cm². The mechanism of corrosion is the corrosive medium gradually penetrates into the composite coating to form micro electric circuit through micro pores, resulting in the increase of porosity and corrosive rate for the composite coating. However, the impedance of epoxy composite coating in substation environment for 18 months is still 2.708×10⁶ Ω·cm², indicating good corrosion resistance.