Outcomes of computer simulation of polymer/silicate nanocomposites mechanical behavior under finite deformation are presented. Nano-filler particles are represented as sheafs from the several parallel ultrathin silicate plates parted by beds of polymer (tactoids), a matrix – as a nonlinear-elastic or elastoplastic material. The stress-strain state round separate inclusion in dependence on its orientation to an exterior load direction and properties of a matrix is researched. The problem of the macro-homogeneous elongation of a periodic cell in the form of the rectangular field with a tactoid at centre has been solved for this purpose. Conditions at which a filler particle loss of a bending stability happens in the course of macroelongation of material are defined. On the basis of the gained solutions the estimate of effective nanocomposite mechanical characteristics depending on properties of a matrix, filler concentration and orientation of corpuscles is spent. Appropriate associations are built.