In　order　to　analyze　main　bearing-capacity　factors　of　shallow　foundation,　Mohr-coulomb　inside-tangent　circle　yield　criterion　and　associated　flow　rule　were　adopted,　the　overall　process　of　foundation　from　elasticity　to　plasticity　gradually　was　modeled　by　elastoplastic　FEM　through　step　increment　method　.　Computed　results　of　several　main　factors　were　compared　and　integrated　with　some　important　results　of　domestic　and　foreign　model　tests.　It　was　shown　that　ultimate　bearing　capacity　of　weightless　foundation　has　slight　relation　with　the　stiffness　and　roughness　of　foundation　while　plasticity-entrance　load　are　obviously　different　due　to　stiffness　and　roughness.　The　destroy　mechanism　of　foundation　was　influenced　greatly　by　the　main　earth　parameter.