Computer model of a polyolefin (thermoplastic) describing its mechanical properties at micro and macro levels is proposed. It takes into account the presence of supramolecular crystallite formations (spherulites) in the structure. These materials (polyethylene, polypropylene, etc.) are semi-crystalline polymers, so their structure is strongly heterogeneous. Spherulites consist of lamellas (flexible thin plates composed of macromolecules laid in transverse loops) and an amorphous phase between them. Lamellas emanate radially from one common nucleus, filling the spherical space around it. Direct analysis of spherulite deformation, taking into account the detailed morphology of the structure, is practically impossible because of its extremely complex geometry. Therefore, a phenomenological approach was used while modeling. Spherulite was represented as a radially anisotropic inclusion, in which the mechanical properties in radial direction were determined by lamellas, and in tangential – by amorphous phase. The spherulitic structure was modeled as a regular lattice of radially anisotropic elastic or elastoplastic inclusions. The hypothesis of the affine nature of structure deformation was also used. That is, it was assumed that the inner regions of the spherulite change their shape as well as the whole one. The degree of spherulite crystallinity (the ratio of crystalline and amorphous phases) was varied by changing its radial and tangential stiffness. Computer simulation was carried out on a hexagonal cell of periodicity. Boundary problems of cell elongation (both in elastic and elastic-plastic formulation) were solved numerically – using the finite element methods. As a result, the dependencies allowing an assessment of the influence of the spherulite structural characteristics on the effective mechanical properties of thermoplastic were constructed.