Abstract: The common relational expression of the relief depth and substrate material of multi-layer diffractive elements in an optical system was derived on the basis of analyzing the diffractive efficiency of mono-layer and multi-layer diffractive elements, and the Abbe number of 20～80 and =0.25～0.6 were obtained by the optimization of these variances. The optical system can achieve high diffractive efficiency in broad wave band by reasonably using multi-layer diffractive elements in optical system. The variances of the relief depth and substrate material of diffractive optical elements are considered in optical system design. The ways to choose the material and relief depth of diffractive elements are described. Three pairs of different material and relief depth elements which can realize the high diffractive efficiency in the broad wave band were designed with the method.