We have developed an approach which allows us to calculate the elastic free energy of the vortex lattice deformed by an external force. In such a case, the minimum of the free energy corresponds to the non-zero displacement u0 with respect to the equilibrium positions of vortices. The free energy of deformed lattice in the elastic approximation should be expanded up to the second order with respect to the displacement in the vicinity of the shifted minimum with non-zero u=u0. We have calculated the elastic matrix of the vortex array deformed by the external force by using the anharmonic terms of the free energy of the unperturbed vortex lattice.