To　improve　the　traditional　finite　element　method　based　on　the　complementary　energy　principle,　an　element　with　the　center　nodes　of　each　side　is　proposed.　The　explicit　unified　expression　of　element　compliance　matrix　and　the　explicit　formulations　for　the　displacements　of　element　nodes　are　derived　from　the　concept　of　base　forces.　The　control　equation　of　the　finite　element　method　expressed　by　the　base　forces　is　obtained　by　using　Lagrange　multiplier　method　of　the　generalized　complementary　energy　principle.　A　finite　element　approach　program　is　developed　using　MATLAB　computer　language.　The　researches　show　that　the　numerical　results　are　consistent　with　those　of　the　theoretical　solutions.