Abstract: The pneumatic moulding is a very complex mechanical process with the features of fast impact, discrete materials, combined geometrical and material nonlinearity. A discrete viscoelastic model for the simulation of incompact molding sand is presented, based on the discrete deformation analysis (DDA) method, and the densification process of the molding sand under air impact is simulated in this paper. The results obtained, in comparison with the corresponding experimental data and the computational results by finite element method, show that the DDA method is applicable for the numerical simulation of the densification process of the molding sand in pneumatic moulding process: the variation tendency of the stress-time curves obtained by DDA is basically consistent with the experimental data, and its error is less than that obtained by FEM, the simulation by DDA is much closer to the reality.