Collapse　is　one　of　the　major　secondary　geological　disasters　induced　by　Wenchuan　earthquake　on　May　12th,　2008.　Based　on　many　on-site　investigations　of　collapse　bodies　in　disaster　areas,　the　movement　process　of　unstable　rock　masses　is　divided　into　three　stages　of　free-fall,　bouncing,　and　rolling.　Mathematical　models　of　the　three　stages　are　established　separately.　Yangjiatai　collapse　body　in　Jiuzhaigou　is　taken　as　an　example.　Its　velocity　of　unstable　rock　masses,　rolling　distance,　and　impact　force　are　calculated.　The　models　can　provide　a　basis　for　the　treatment　design　of　the　collapse　bodies　in　the　disaster　reconstruction　process.