Abstract: In order to evaluate the service performance of 317L stainless steel in the offshore waters of the South China Sea and to ensure the safe operation of underwater oil and gas production facilities, natural seawater corrosion tests were carried out. The electrochemical testing, corrosion morphology observation, microbial detection and other methods were combined to characterize the corrosion characteristics and corrosion resistance changes of 317L stainless steel during service. The results indicate that 317L stainless steel posed a risk of pitting during long-term service in the detention environment near the South China Sea. The dynamic balance between the dissolution and repair of the stainless steel passivation film was disrupted by the combined action of Cl^- and microorganisms. The autocatalytic reaction of the corrosion blocking battery led to accelerating activation and dissolution of the matrix in the corrosion pit, increasing the risk of pitting.