The finite difference equation is developed, which may be used to calculate the electric field of the inhomogeneous anisotropic medium. The validity of the equation is tested. The distributions of the electric potential and the electric field are presented for an anisotropic trihedron body. Its Rayleigh scattering property is researched. Simulations show that the dielectric constant in the polarizing direction of the incident electric field has an obvious impact on scattering, the dielectric constant in the perpendicular direction has not much effect on it. The arithmetic is not confined by the factors such as the target's shape and electric parameter etc. and has the peculiarities of briefness and versatility.