When initial density and confining pressure of non-cohesive soil are considered in Pastor-Zienkiewicz (PZ) constitutive model, multiple sets of parameters are required to simulate the same type of material. Thus this model is pretty difficult to be applied in practice, which to a great extent limits its development. To solve the existing deficiency of the PZ model, some recently proposed state parameters are introduced into the dilatancy formula, plastic potential direction vector, loading (unloading) direction vectors and plastic modulus equation of the original PZ model, separately. It is found that the predicting capability of the modified model has been improved in terms of mechanical behaviour of the non-cohesive soil, particularly by considering the initial density and confining pressure. Then the calibrating method for each parameter in the modified model is discussed in detail and the physical meaning of each parameter is further clarified, according to a practical example. Finally, the predictive ability of the modified model is verified by the experimental data. It is shown that predicted results are in good agreement with experimental data, which indicates the modified model is reasonable and feasible.