The compression characteristics of green sand were investigated experimentally, including the squeezing and yielding during deformation. An expression was developed for the transient compression modulus of sand during compression. Based on the hypothesis put forward of the compression state, the differential equation for the nonlinear constitutive equation was deduced by introducing a move-yield poten- tial function. The state constitutive equation under the tri-axial experiment is further studied according to the sand attributes, considering the differential form of Hooke’s law and the Mohr-Coulomb condition. The re- lated experiment data are applied to verify the proposed constitutive model of sand. The compression characteristics of green sand were investigated experimentally, including the squeezing and yielding during deformation. An expression was developed for the transient compression modulus of sand during compression. Based on the hypothesis put forward of the compression state, the differential equation for the nonlinear constitutive equation was deduced by introducing a move-yield poten- tial function. The state constitutive equation under the tri-axial experiment is further studied according to the sand attributes, considering the differential form of Hooke’s law and the Mohr-Coulomb condition. The re- lated experiment data are applied to verify the proposed constitutive model of sand.