doubly clad optical fiber with an inner cladding made of birefringent single crystal whose optical axis is parallel to the fiber axis is discussed. Exact characteristic equations are derived for vector modes. The influence of the ratio (KCl) of the ordinary ray refractive index to the extraordinary ray index upon the waveguide dispersion is analyzed in detail. It is impossible to deduce the expression of waveguide dispersion because of the complexity of the characteristic equations, a feasible approach to calculate the waveguide dispersion is presented. The results show that with the change of k cl , the value of waveguide dispersion changes correspondly as the geometrical and optical parameters (S and R) keeping invariable. The influences made by k cl , S and R on the propagation and cutoff characteristics of low order modes are also analysed. The result provide a significant reference for designs of new types of dispersion flattened fiber, dispersion shift fiber and passive optical devices