Abstract: Based on the analysis of the salt fog environment in the Hainan launch site and its origins, as well as a statistical analysis of the chloride content in the coastal atmosphere, this paper studies the effect of the salt fog environment on several typical spacecraft structural materials, as expressed by their microscopic appearance, the surface composition, and the XRD pictures taken after a one-year exposure test. The degradation of the thermal control function of the ZK61M magnesium alloys is analyzed. An assessment of the comprehensive effect for the pre-launch test and the after-launch flight period is made. It is indicated that no observable erosion would occur during an average pre-launch test period of three months, and that the salt fog contents such as the chlorine ions on the surface of those structural materials would not likely to get deeper or expand.