Discrete　optimization　is　converted　into　continuous　optimization　using　mechanics　mapping.　A　two-node　model　is　constructed　close　to　the　optimal　result　of　continuous　optimization.　The　optimization　of　shell　structures　is　thus　achieved　using　variable　linking　and　the　infinitesimal　multiple-node　element.　Meanwhile　discrete　optimization　module　is　developed　with　PCL　language　based　on　Nastran　software　and　several　examples　are　optimized.