With　the　rapid　development　of　economy　and　tourism,　Dong　Changyu　tunnel　which　have　single　lane　has　been　unable　to　meet　the　increasing　traffic.　Due　to　the　terrain　and　geological　conditions,　it　is　unable　to　build　a　new　one,　there　is　only　way　to　expand　the　existing　tunnel.　Based　on　blasting　excavation　of　collapse　cavity　section,　this　paper　analyzes　rock　fragmentation　and　blasting　vibration　of　multi　free　surface.　Using　numerical　calculation　method　with　Lagrangian　algorithm　and　full　restart,　it　simulates　the　effect　of　blasting　vibration　on　the　reinforcement　area　of　collapse　cavity　and　the　surrounding　rock,　and　obtains　vibration　velocities　and　its　law　of　characteristic　points.　Compared　to　the　field　experiments,　the　vibration　velocities　of　numerical　simulation　are　close　to　them.　The　results　indicate　that　the　numerical　calculation　method　can　descripts　rock　fragmentation　and　blasting　vibration　in　the　millisecond　delay　blasting.　The　research　has　reference　and　guidance　for　similar　engineering.　©　2016　Taylor　&　Francis　Group,　London.