Two-phase　control　means　that　middle-variables　are　inserted　between　natural　design　variables　and　nodes　in　the　mesh.　Two-phase　control　is　established:　1)　The　coordinates　of　the　key　points　are　controlled　by　natural　design　variables;　2)　The　nodes　in　the　FEM　mesh　are　controlled　by　key　points.　The　second　control　describes　the　design　elements　in　terms　of　the　shape　function　of　FEM　and　the　parameter　coordinates　are　introduced.　Then　the　sensitivity　analysis,　the　control　of　change　of　structural　shape　and　its　mesh　are　realized.　On　the　base　of　the　two-phase　control,　some　difficulties　in　the　problem　of　shape　optimization　can　be　solved　and　the　problem　is　approached　as　a　Sequential　Quadratic　Programming　problem　to　be　solved.　The　program　of　shape　optimization　is　carried　out　on　MSC/PastraneV-Nastran　platform　and　by　using　PCL　language.　The　idea　of　the　research　is　verified　by　some　examples.　The　reliability,　the　accuracy　and　the　high-efficiency　of　the　program　have　been　testified　by　the　results　of　the　examples.