Liquid crystals(LC) with unique physical and chemical characteristics, such as electric and magnetic anisotropy, and demonstrated as optical uniaxial crystal. When the liquid crystal system applied with magnetic field, the director will change its direction with variation of the magnitude of the magnetic field. In this paper, we study the optical modulated effect of nematic liquid crystal molecules arranged along the surface with the continuum elasticity theory model. We also use the finite difference numerical method to simulate the distribution of the liquid crystal molecules and the birefringence effect of liquid crystal, which will further our understand of polarization apparatus based on liquid crystal.