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During the exploitation of oil and gas fields, the internal environment typically contains large amounts of a mixture of H2S and CO2 gases. The coexistence of H2S, CO2, and Cl- poses a potential threat of pitting corrosion to stainless steel. In a Cl-erosion environment with high H2S-CO2 gases, the anodic dissolution rate of 316L steel increases, destroying the passivation film and resulting in pitting. In a Cl- corrosion environment with high H2S-CO2 gas concentrations, both H2S and CO2 can reduce the stability of the stainless steel passivation film, with H2S having a more severe impact on pitting corrosion. As the pitting pits continue to expand, Cl- accumulates within them, accelerating their growth in a vertical direction. Under tensile stress, the sensitive areas at the bottom of these pitting pits can serve as crack initiation sites for stress corrosion cracking, allowing the cracks to spread further. Simulations of H2S-CO2-Cl- environment tests in an autoclave demonstrated that the tensile strength of 316L stainless steel gradually decreases as the Cl- content increases; under the effect of Cl- pitting, its fracture behavior shifts from ductile fracture to brittle fracture. Distinct ductile pits are present in the absence of Cl- and at low Cl- concentrations, indicating transgranular fracture ； As the Cl- content increases, the fracture morphology exhibits a cleavage characteristic, which is intergranular fracture. This indicates that Cl- is the key factor causing slow tensile stress corrosion in 316L stainless steel. Therefore, in oil and gas field environments, stainless steel is subject to severe pitting corrosion as a result of the combined effect of H2S, CO2, and Cl-. However, the corrosion mechanism of stainless steel under the combined action of H2S, CO2, and Cl- is very complex; currently, most scholars still have disagreements regarding the patterns and mechanisms of pitting corrosion, and further in-depth research and analysis are needed.