We have used the Structural Diffusion Models (SDM) to calculate the pair distribution function, for fluid argon, A general recipe is developed for analysing structural data by such models. First, we analyse fluid argon in terms of the local Structural Diffusion Model (SDM1). The SDM parameters obtained by constrained optimization describe the dependence of the pair distribution on density and temperature. Second, we use an extended version of the model (SDM2) and it enables us to obtain a refined fitting through a built in contraction function f(r). A simple choice for f(r) in the model expression of g(r), applied the two dense lattices, gives an improved fit for high densities. The best results are obtained with the hcp lattice.