[en] The possibility for the observation of muon spin precession in various magnetic phases of rare-earth metals of the heavy group is investigated theoretically. The precession of the muon spin stopped in interstitial site of a crystal lattice is described by the solution of the classical equation. The local magnetic field vector in interstitial sites consists of dipole and hyperfine components and forms the axis for muon spin precession. Functions for time dependence of muon polarization for cases of the longitudinal spin wave as well as simple and ferromagnetic spiral structures are obtained on the basis of averaging the solution of precession equation over various interstitial sites in the crystal lattice. The connection of the precession frequency under observation with microscopic parameters of the magnetic substances is obtained