In　traditional　construction　safety　assessment,　it　is　difficult　to　describe　the　safety　status　of　different　construction　stages.　To　solve　this　problem,　this　paper　proposes　a　digital　twin　modeling　theory　for　construction　safety　assessment.　Firstly,　this　paper　analyzes　the　requirements　of　a　digital　twin　model.　Secondly,　the　required　information　is　collected　by　IoT.　Finally,　the　DT　model　is　established　based　on　the　collected　information.　This　DT　model　analyzes　the　collected　information　by　ML,　which　aims　to　conducting　the　assessments　of　construction　safety.　To　verify　this　method,　this　paper　analyzes　the　vault　settlement　during　tunnel　construction.　The　analysis　results　show　that　the　DT　model　can　predict　the　settlement　value　with　high　accuracy.　Moreover,　the　safety　state　is　assessed　dynamically　based　on　the　settlement　value　by　DT.