The computer modelling algorithm is presented for a microstructure of the granular composite materials. Outcomes of computer synthesis of the granular composites microstructures are given taking into account different number of structural elements (grains). The received microstructures differ from each other average sizes of grains and their distributions law. Laws of distributions of grains sizes are tested by means of shear-scale invariants criterion. By means of method of statistical modelling is carried out the analysis of this criterion power at different alternatives. The comparative analysis of this criterion with Kolmogorov-Smirnov criteria and a chi-squarecriteria is given. The results of numerically simulate of deformation and fracture of granular composites are given.