A　nonlinear　exist-null　combined　body　is　proposed　to　raise　the　efficiency　of　the　searching　optimum　solution　of　structural　topology　optimization　based　on　a　physical　model.　As　an　example　of　topology　optimization　for　a　frame　structure,　a　mathematical　model　for　the　minimization　of　structural　weight　is　implemented　to　realize　in　procedure　coding.　In　different　with　the　linear　exist-null　combined　body,　the　nonlinear　one　is　a　combination　with　infinite　numbers　of　infinitesimal　exist　cells　and　nulls　cells　according　to　their　nonlinear　lengths.　Owing　to　invariance　property　in　sum　of　lengths　between　exist　cells　and　nulls　cells　for　each　beam　element,　its　topological　variable　can　be　expressed　by　total　lengths　of　its　exist　cells.　Structural　weight　and　displacements　constraints　are　deduced　to　build　an　optimization　model.　The　model　is　solved　by　the　algorithm　of　the　linear　programming　to　show　the　increasing　efficiency　of　an　optimizing　point.　The　comparison　of　ICM　(Independent,　Continuous　and　Mapping)　as　a　mathematical　transformation　method,　the　physical　model　presented　has　also　different　approaches　but　equally　satisfactory　results.　A　nonlinear　relationship　in　length　of　the　latter　replaces　the　filter　functions　of　element　weight　and　displacements　constraints　of　the　former.　Similarities　and　differences　between　the　mathematical　transformation　method　and　the　physical　model　method　are　an　interesting　problem　affording　for　thought.