Theoretical　analysis　and　numerical　are　used　to　investigate　the　critical　velocity　in　tunnel　cross-passage.　Considering　the　effect　of　train　blocking,　several　cases　are　built　by　FDS　to　verify　whether　the　critical　velocity　can　control　the　smoke　in　the　cross-passage.　Result　indicates　that　the　distance　of　the　train　head　away　from　the　cross-passage　as　1/2　power　of　the　tunnel　velocity.　With　the　train　crossing　the　cross-passage,　the　value　velocity　of　the　cross　door　increase　gradually　and　then　decreases　when　the　middle　of　the　train　stocking　in　the　door　of　cross-passage.　The　maximum　value　of　velocity　is　greater　than　the　critical　velocity　calculated　by　Froude　model　and　the　smoke　diffuse　to　the　cross-passage.　In　other　cases,　the　velocity　fails　to　prevent　the　soot　propagation　from　accident　side　of　the　tunnel　and　the　gas　full　of　the　cross-passage　cause　risk　of　evacuation.　(C)　2016　Published　by　Elsevier　Ltd.