Along with the increasing pace of marine resource development and strategic deployment of China, the infrastructure materials and deployed aircraft were facing severe salt fog corrosion during the construction process of the South China Sea. Materials damage in this environment is much more serious than that in other marine atmospheric environment. Owing to its location near the equator and the direct impact of solar radiation, Nansha marine atmosphere is a representative and typical climate with high temperature, high humidity, high salinity and high radiation. However, there has been lack of material corrosion data and relevant fundamental research until now. Carbon steel is usually one of the most widely used infrastructure materials and reference materials, and its corrosion data exposed to Nansha Islands marine atmosphere is much more important. These corrosion data can not only provide important basis for environmental corrosivity category, but also provide reference for indoor accelerated corrosion test. Therefore, in order to obtain useful information on selected construction materials, adopting the appropriate corrosion protection methods, and predicting the life of metallic structures under service, the exposure test was conducted on carbon steel Q235 and weathering steel Q450NQR1 in Nansha Islands for 2 and 5 months. Thickness loss analysis, macroscopic observation, SEM, XRD, optical profiler and tensile tests were conducted to study the initial corrosion behavior on both sides of Q235 and Q450NQR1 in Nansha marine atmosphere. The results showed that the initial corrosion behavior of both steels at this site was more serious than those at most areas, such as Wanning and Xisha Islands, and the corrosion of skyward of both steels was more serious than that of field-ward. The rust layer formed on field-ward was easier to fall off. After exposure for 2 months, the thickness loss of Q235 was the same as that of Q450NQR1, and corrosion products on both sides were mainly composed of γ-FeOOH, α-FeOOH and Fe₃O₄; while after 5 months' exposure, the thickness loss of Q235 was much larger than that of Q450NQR1, and corrosion products were mainly composed of γ-FeOOH, α-FeOOH, Fe₃O₄ and β-FeOOH. The relative composition of β-FeOOH and γ-FeOOH was fewer on the field-ward, and the relative composition of Fe₃O₄ was fewer on the skyward.