Automatic　reconstruction　of　unknown　3-D　objects　has　been　of　great　importance　in　the　areas　of　machine　vision,　object　recognition,　and　automatic　modeling.　In　this　paper,　a　new　planning　approach　of　generating　3-D　models　automatically　is　proposed.　The　new　algorithm　incorporates　the　limit　visual　surfaces　of　unknown　model　which　are　obtained　according　to　both　of　the　known　object　boundary　knowledge　and　the　visual　region　of　the　vision　system　and　selects　the　suitability　of　viewpoints　as　the　next　best　view　on　scanning　coverage.　The　limit　visual　surfaces　are　used　to　predict　the　maximal　information　of　unknown　model　and　then　the　visibility　criterion　of　next　viewpoint　is　determined.　And　the　position　which　can　obtain　the　maximal　visual　surface　area　is　defined　as　the　next　best　view　position.　The　reconstruction　result　of　real　model　with　proposed　method　show　the　efficiency　in　practical　implementation.