An improved method for measurement of complex permittivity using six-port reflectometer is presented.Error caused by incomplete superposition between the measured plane and reference plane,which is often in the case of conventional measuring method,is eliminated with the developed novel algorithm by separating the two planes.The simple and accurate numerical solution of the transcendental equation is given.The relationship between multivalued spacing of relative permittivity,measuring frequency and length of the sample has been gained.Some experimental results have validated the efficiency and practicability of the proposed method.