• Grain refinement was avoided through modified LPwC. • Compressive residual stress after LSP reduces the metastable pitting rate. • Microdefects induced by LSP dominate the growth of metastable pits. • Adjacent metastable pits combine easily to transform into a stable pit after LSP. Laser shock peening (LSP) was performed on a 316 stainless steel for microstructural and mechanical modifications. To identify the dominant factor controlling pitting corrosion resistance, a single LSP impact was performed and various characterization techniques, such as scanning electron microscopy, X-ray diffraction, transmission electron microscopy, electron backscattered diffraction, microhardness and residual stress analysis were conducted. The results show that a considerable increase in the microdefects, microhardness, and compressive residual stress occurred at a depth of ∼200 μm from the surface, while no evident grain refinement was observed. The compressive residual stress reduced the metastable pitting nucleation rate. However, microdefects after LSP treatment resulted in larger metastable pits, which are more likely to combine to transform into a stable one. It is summarised that the substantial microdefects can deteriorate the superiority of compressive residual stress induced by LSP in the pitting resistance of 316 stainless steel.