The initial failure process of the powder spraying coating (namely 60% polyester, 10% TiO₂, 7% curing agent, 6% leveling agent, 2% pigment, 15% auxiliary materials), which was applied on 316 stainless steels, in artificial coastal atmosphere and seawater was investigated by electrochemical impedance spectroscopy (EIS) technique, whilst the failure process was analyzed. The results showed that in the artificial coastal atmosphere, the coating resistance decreased from an initial value of 1.07 × 10⁸ Ω·cm² to 1.48 × 10⁶ Ω·cm² over the first 96 hours by a descent rate of 1.10 × 10⁶ Ω·h^-1. In the artificial seawater, the coating resistance decreased from an initial value of 1.56 × 10⁸ Ω·cm² to 1.99 × 10⁶ Ω·cm² over the first 48 hours by a descent rate of 1.30 × 10⁶ Ω·h^-1. Whether the coated steels expose in the artificial coastal atmospheric environment or immerse in the artificial seawater, the lnC_c-t^1/2 curves for coatings indicated that the coating capacitance presented two typical stages as the corrosion time increased, the coating capacitance increased rapidly in the beginning time of corrosion, and then tented to be a slow growth. Furthermore, the water molecular diffusion coefficient D for the powder spraying coating in the artificial coastal atmosphere was 1.69 × 10^-11 cm²·s^-1, while that was 2.31 × 10^-11 cm²·s^-1 in the artificial seawater, which is slightly higher than that in the coastal atmosphere.