In this paper, the ideal normal mode characteristic equation of the optical fiber with uniaxial anisotropic crystal cladding is derived. Using mean value theorem and combining Matlab numerical method, a solving algorithm of this transcendental equation is proposed. Therefore, the relationship between FBG reflect spectrum characteristic and cladding reflective index is simulated. The simulation results show that kcl has a strong influence on the spectrum, different values of kcl can lead to different reflectivities and different Bragg wavelengths.