Abstract: A series of safety protection measures, including safety instrument system (SIS), are equipped for natural gas processing device. At present, the conventional safety integrity level (SIL) evaluation method is mainly applied to determine whether the SIS in design or production plant in service could meet the safe production. In the paper, the characteristics of SIL assessment and the relationship of SIL, hazard and operability analysis (HAZOP), and asset integrity management are analyzed, and the significance of SIL evaluation is discussed. At the same time, a method of SIL evaluation is proposed, and the changing is introduced from the method to SIL evaluation software. Application results show that, in theory, it is feasible to convert the conventional SIL evaluation method into the SIL evaluation software. Once the strong SIL evaluation software being applied, the investment of human and financial resources would be greatly reduced in SIL evaluation, and the evaluating results would be more objective and credible.