According to birefringent effect of uniaxial crystal and principle of polarization interference, the design principle of Lyot filter is analyzed by using Muller matrix. The theoretical analysis shows that the rational values of the thicknesses to the minimum thickness among the plates in the filter are possible to be non-integer. Several design examples of four-stage Lyot filter which have thickness in a non-integer and integer ratio are given, together with a brief discussion and comparison about their transmission curve.