Abstract <p>The study of microplastic strain accumulation processes under complex passive loading is relevant for fatigue analysis. In this paper, based on a modified microstructural model of elastoplastic deformation, which includes various mechanisms of inelastic deformation, the possibility of a refined description of non-proportional passive loading is investigated, and the proposed approach is experimentally verified. The microstructural model of polycrystalline material takes into account the presence and interaction of crystallites with arbitrary orientation. The model is compared with the experiment using the finite element homogenization method by averaging the microstress and microstrain fields over a representative volume element. The results of experimental studies of tubular polycrystalline samples of technically pure nickel under active (uniaxial tension after preliminary compression) and passive (torsion with tension/compression inside the yield hypersurface) loading are presented. A&#xa0;relation between the microstructure of the samples and their mechanical characteristics has been established. Based on the results of macro-level experiments using the <i>particleswarm</i> optimization method, which simulates the group behavior of agents, a procedure for determining the parameters of the microstructural model has been developed. The comparison of computation results with experimental data showed that the proposed two-level microstructural model of polycrystalline material allows the process of plastic strain accumulation under complex non-proportional passive loading to be described with good accuracy.</p>