Abstract: In response to the long-term anti-corrosion requirements of marine photovoltaic fasteners in high-salt and high-humidity environments, the differences in microstructures, mechanical properties, and corrosion resistances between the multi-alloy co-diffusion layers and hot-dip galvanized layers are systematically compared, to provide a basis for the selection of fastener protection technologies in extreme environments. The layer formed by multi-alloy co-diffusion exhibits a smooth surface morphology (Ra=1.2 μm), the surface thickness distribution (standard deviation≤1.8 μm) is controllable, and the microhardness reaches 472.9HV0.05, 48% higher than that (320.0HV0.05) of the hot-dip galvanized layer. No corrosion is observed after 500 hours of neutral salt spray testing, and only surface color changes slightly after 500 hours of acid salt spray testing. After 7 days of cyclic immersion, only slight surface rust appears, and the weight loss ratio (0.9 mg/cm²) is 90% lower than that (8.7 mg/cm²) of the hot-dip galvanized layer. Multi-alloy co-diffusion technology significantly outperforms hot-dip galvanizing in terms of coating uniformity, hardness, and corrosion resistance, demonstrating significant engineering application value in marine photovoltaics for extreme environments.