Abstract: Basic properties of constitutive relation and densities of energy for the elastic body are analysed.Hu-Washizu principle/Hellinger-Heissner principle is redemonstrated,applying Lagrange multiplier method,based on the principle of minimum potential/complementary energy.The re-demonstration show that H-W principle is a principle either of three-field with undetermined multipliers or of two-field with eliminated multipliers and H-R principle is a two-field principle,the multipliners of which are undertermined or eliminated.