Abstract: Poisson’s ratio is a key parameter in the phenomenological constitutive models of closed-cell aluminum foam. In order to resolve the divergence in understanding the change law of closed-cell aluminum foam Poisson’s ratio and understand the physical meaning of the characteristic points in the closed-cell aluminum foam Poisson’s ratio change rule, the numerical simulation method is used. The 3D-Voronoi model and 2D-Voronoi model of closed-cell aluminum foam are established and simulated under the boundary condition of lateral displacement coupled uniaxial compression. Based on the phenomenological characteristics of the closed-cell aluminum foam constitutive model, it’s also very important to study the deformation patterns of the closed-cell aluminum foam. In order to clarify its deformation patterns under triaxial compression, the 3D-Voronoi model of the closed-cell aluminum foam is simulated under the boundary condition of lateral displacement limited axial compression. The results show that the thickness reduction characteristic in the contact of conventional shell elements is the reason for the divergence of the Poisson’s ratio of closed-cell aluminum foam, however, the thickness reduction does not affect the deformation mode of the cell structure of the aluminum foam model before densification; the accurate change law of the Poisson’s ratio of closed-cell aluminum foam is an “S” curve of “increasing-decreasing-increasing again”, and the maximum value of the curve corresponds to the deceleration point of the energy absorption efficiency growth; in the state of proportional axisymmetric loading paths, closed-cell aluminum foam has four lateral deformation patterns, namely, “(short-term) compression→expansion”, “compression→expansion→compression→expansion”, “compression→(short-term) expansion” and “compression”.