The invention relates to an SIL (safety integrity level) assessment unit for a safety-instrument system for an LNG (liquefied natural gas) project. The SIL assessment unit comprises a project information management module, an HAZOP (hazard and operability analysis) result import module, an intermediate data management module, an SIL assessment calculation module, a database management module and an assessment result output module, wherein the project management information module is used for building an SIL analysis project; the HAZOP result import module is used for carrying out structured processing on the HAZOP analysis result of the SIL analysis project by taking a plot as a unit; the intermediate data management module is used for managing, inquiring and editing HAZOP analysis plots stored in the HAZOP result import module; the SIL assessment calculation module is used for carrying out assessment calculation aiming at each input HAZOP analysis plot by adopting an LOPA (layer of protection analysis) method, and obtaining the to-be-set SIL; the database management module is used for providing the acceptable risk frequency of an influence event, the initial event occurrence frequency and the failure probability reference value of an independent protective layer which are required for LOPA analysis; the assessment result output module is used for automatically generating an SIL assessment report. The SIL judgment method can be widely applied to SIL assessment of the safety-instrument system for the LNG project.