The first excitation energy and the mean number of phonon of the strong-coupling magetopolarons in the polyatomic semi-infinite polar crystals were studied through a linear-combination operator and unitary transformation.When the electron is approaching infinitely to the surface of crystals

the results show that when the magnetic field is strong

the first excitation energy of the magnetopolaron is only twice the Landau ground state energy

and the mean number of phonon is equal to the number of LO phonons and that of SO phonons that each one has coupling with the electron;and when the magnetic field is weak

the first excitation energy of the magnetopolaron is other four sections nothing the Landau ground state energy

and the mean number of phonon is equal to the contributions of LO phonons and that of different LO phonons that each one has coupling with the electron and magnetic field.When the electron is situated in the depth of crystals

the results show that when the magnetic field is strong

the first excitation energy of the magnetopolaron is equal to the twice Landau ground state energy and the double add energy of LO phonons that each one has coupling with the electron and magnetic field

and the mean number of phonon is only the contributions of LO phonons with its frequency and the magnetic field that each one has coupling with the electron;and when the magnetic field is weak

the first excitation energy of the magnetopolaron is other six sections nothing the Landau ground state energy

and the mean number of phonon is the double contributions of LO phonons and that of different LO phonons that each one has coupling with the electron.