Abstract: In the petroleum and petrochemical industry,the security of industrial control systems directly affects whether the equipment can operate stably and whether the entire production process can proceed smoothly. In the whole life cycle of system construction and operation,the assessment and verification of safety integrity level （SIL） for safety instrumented system （SIS） are core links in ensuring process safety. Combined with engineering practices in the petroleum and petrochemical industry,this paper systematically analyzes the key methods for SIL determination and verification,and proposes targeted optimization schemes through the quantitative evaluation process of typical cases,thereby providing feasible technical paths for ensuring process safety.

Key words: SIL, safety instrumented system, Layers of Protection Analysis （LOPA）, Risk Reduction Factor （RRF）