Abstract: The variational problem related to the coupled vector wave equations and boundary conditions of circular dielectric waveguide with arbitrary refractive index profile is solved by using the finite element method (FEM). This method can be used to calculate the mode field for different refractive index profile optical fiber with high precision without any limitation of weakly guiding or Guass Mode field distribution to the dielectric waveguide. The normalized mode field and power proportion inside the core are also studied under different structure parameters of triangular segmented core with step ring optical fiber by this method.