Using the algebraic method of the theory of angular momentum in quantum mechanics a detailed study is made for the model of s-f interaction of rare-earth metals. A general form of Hamiltonian of s-f interaction is derived. Utilizing the method of the theory of perturbation in operator form we have obtained the general expression for the effective Hamiltonian of f-f interaction through s-f interaction. Retaining terms to the second order of smallness, besides the isotropic exchange interaction the pseudo-dipole interaction is also obtained. On the basis of the results obtained, we have discussed preliminarily the magnetic crystalline anisotropy of the ferromagnetic phase of rare-earth metals. Some experimental facts which might be explained by the above results are indicated.