Abstract: Hazard and operability analysis (HAZOP) method, as a qualitative hazard analysis method, is difficult to quantify the residual risk. On the basis of that, safety integrity level (SIL) analysis techniques are introduced and briefly described, which include the safety instrumented system (SIS), SIL, and the two steps of SIL analysis: SIL classification and SIL verification. Then, three methods, such as risk matrix, risk map and layers of protection analysis (LOPA), of SIL classification are introduced, as well as the key points of SIL verification. Besides, choosing an interlocking system of in-service device, the process of SIL classification and SIL verification are carried out by examples, and the final results are analyzed. In the end, the article combed the precautions of carrying out the SIL analysis.