The supercell model for the Bragg fibers is proposed for investigating the mode characteristics and propagation properties. The transverse refractive index profile is expressed by Fourier series, and the energy band structure is obtained by the plane wave expansion method. The mode propagation constant and the expansion coefficients of the electric field can be obtained from the eigen system which is deduced from the full-vectorial coupling wave equations based on the localized orthogonal Hermite-Gaussian functions. The supercell mode is implemented when the high-index core Bragg fiber is taken into account. Some lower-order modes are analyzed, and the mode birefringence of the fundamental pairs can be used to scale the accuracy of this algorithm. The supercell model is also efficient for the hollow core Bragg fibers.