This　paper　proposes　a　new　assessment　method　for　lightning　trip-out　of　transmission　lines　that　includes　an　improved　analytic　hierarchy　process　(IAHP)　algorithm　based　on　a　lift　in　association　rules.　First,　the　k-means　clustering　algorithm　is　used　to　discretize　the　geomorphic　information　along　transmission　lines,　and　ten　feature　factors　are　obtained.　Next,　by　analysing　the　correlation　between　each　feature　factor　and　a　lightning　trip-out　event　using　the　lift　algorithm,　the　strong　correlation　factors　are　extracted.　On　this　basis,　an　IAHP　algorithm　optimized　by　lift　is　proposed　to　establish　an　objective　judgment　matrix.　Then,　multiple　indexes　are　combined　as　a　criterion　layer　of　the　IAHP,　and　a　lightning　risk　assessment　model　of　transmission　lines　is　established.　Finally,　the　proposed　method　is　validated　by　simulations　using　28　transmission　lines　with　220　kV　voltage　grade　of　a　provincial　power　grid　of　China.　An　assessment　model　is　established　using　the　lightning　trip-out　data　in　the　period　2010-2014,　and　then　this　model　is　employed　to　estimate　the　lightning　trip-out　risk　in　the　period　2015-2018.　Based　on　the　number　of　phase　faults,　the　agreement　between　the　estimation　results　and　the　actual　values　is　76%.　The　proposed　model　provides　a　new　method　for　the　lightning　risk　assessment　of　transmission　lines.