This　paper　reviews　two　major　models　(small　displacement　torsor,　Deviation　and　clearance　domain)　for　3D　functional　tolerance　analysis　and　compares　them.　the　underlying　mathematical　representation　of　geometric　tolerances　can　be　classified　as　inequalities　and　multi-variate　region.　the　corresponding　algebraic　or　geometric　tolerance　propagation　mechanism　of　each　model　is　briefly　introduced　for　worst-case　and　statistical　tolerancing.　through　a　comprehensive　comparison　of　these　models,　This　paper　gives　some　suggestions　for　choosing　the　appropriate　method　for　a　given　tolerancing　problem.　©　(2013)　Trans　Tech　Publications,　Switzerland.