Abstract: Abstract The mechanical swivel on a certain marine submersible release device broke, and there was a large gap on the surface of the release buckle connected to the mechanical swivel. The causes of mechanical swivel fracture were analyzed using macroscopic observation, scanning electron microscopy and energy spectrum analysis, point corrosion testing, metallographic examination, chemical composition analysis, hardness testing. The results show that the material of the bolts in the shackle was 316L stainless steel, which mainly underwent point corrosion in marine environments, resulted in a decrease in the hardness of the bolts and swivel rings, and the generation of stress cracked. The cracks continued to propagate, ultimately led to the fracture of the mechanical swivel.