Modeling strength properties of composite materials (CM) of structure [±f]c in case of a combination of the two-dimensional stress state (or plane strain) and in-plane shears is carried out with use of methods of resistance of materials and theories of plasticity. It is used rigid-plastic model of a deformable solid body. It is shown, that if the surface of strength for a monolayer is described by the quadric equation, that, in generalized case, the surface of strength for CM of structure [±f]c in case of a two-dimensional problem also is a quadric surface, and at in-plane shear – is not present. Procedures of approximation both the surface of strength for CM, and its certain sections are offered. Examples of calculations are resulted. Results are generalized for the hybrid CM having a plane of symmetry of structure and properties.