The properties of a strong coupling magnetopolaron in polar crystals are studied using a linear combination operator.The influence of the electron spin on the ground state energy and the effective mass of a strong coupling magnetopolaron in polar crystals are discussed.Numerical calculation for CsI crystal show that the ground state energy of the strong coupling magnetopolaron increases or decreases with increasing magnetic field when electron spin points at different directions,and the influence of electron spin on the ground state energy of the strong coupling magnetopolaron increases with increasing magnetic field.