Abstract: In the natural seawater medium, the microstructure of 310S stainless steel and 800H stainless steel was analyzed and compared by metallographic microscopy, scanning electron microscopy, laser confocal microscopy and atomic force microscopy, and the corrosion law of these two stainless steels in the natural seawater environment was studied by immersion test and electrochemical test. The results show that the microstructure of 310S stainless steel and 800H stainless steel was austenitic, and both had second phase precipitation, the precipitate phase of 310S stainless steel was mainly Cr-rich carbides and carbon and nitrogen compounds, and the precipitated phase of 800H stainless steel was mainly Cr-rich carbides and Al and Ti carbon and nitrogen compounds. After electrochemical testing in natural seawater medium, there were obvious corrosion traces on the surface of 310S stainless steel and 800H stainless steel. Due to the addition of Al, Cu and Ti alloying elements in the 800H stainless steel, the corrosion resistance of 800H stainless steel is better than that of 310S stainless steel.