This　paper　numerically　studies　the　anti-collapse　behavior　of　the　modular　steel　building　(MSB)　in　the　scenario　of　interior　module　removal　and　corner　module　removal.　The　vertical　displacement,　lateral　displacement　and　internal　force　of　a　six-storey　MSB　in　a　sudden　module　loss　are　studied.　The　reasonability　by　using　rigid　body　assumption　in　collapse　analysis　of　the　MSB　is　examined.　A　refined　fracture　model　of　the　steel　is　incorporated　into　ABAQUS　via　user　subroutine,　in　which　the　effects　of　both　stress　triaxiality　and　Lode　angle　on　the　fracture　ductility　of　the　steel　are　considered.　In　the　pushover　analyses,　the　effects　of　the　horizontal　connection,　opening　of　the　wall　panel　and　thickness　of　the　wall　panel　on　the　collapse　resistance　and　failure　mode　of　the　MSB　are　studied.　The　dynamic　amplification　factor　(DAF)　of　the　MSB　at　the　collapse　limit　state　is　also　obtained.　It　is　found　that　the　rigid　body　assumption　may　significantly　underestimate　the　displacement　and　maximum　shear　force　in　the　horizontal　connection　of　the　MSB.　Two　types　of　failure　modes　of　the　structure　are　observed,　namely,　connection　failure-induced　collapse　and　module　unit　failure-induced　collapse.　Among　the　studied　parameters,　the　effect　of　the　opening　size　of　the　wall　panel　on　the　behavior　of　the　structure　is　the　most　significant.　In　the　scenario　of　the　interior　module　removal　and　corner　module　removal,　the　DAFs　of　the　structure　at　the　collapse　limit　state　range　from　1.20-1.29　and　1.27-1.50,　respectively.