Classic theory is not suitable for the calculation of composite materials with high duty factor, an algorithm of the effective permittivity of composite materials using the equivalent capacitance is presented. The packing mediums in the capacitor are the particle dispersion type composite materials. By solving the equivalent capacitance of the capacitor, the formulas of effective permittivity are derived. By comparing the model with MG model and EMA model, the results are very similar, so this algorithm is correct and adaptable，the results are matched with the experimental values given in the literatures under the case of high duty factor.