In this study, a mathematical model of the relationship between the bandwidth integral diffraction efficiency (PIDE) and the incident angle with the substrate material of a multilayer diffractive optical element (MLDOE) for a two-band system is established. A method for selecting a double-band oblique incident MLDOE substrate material is proposed; this method selects the best base material combination of the dual-band MLDOE. The proposed method and the mathematical model solve the problem in which the improper selection of the substrate material leads to a decrease in the diffraction efficiency and bandwidth integral diffraction efficiency of the MLDOE when light is obliquely incident. In addition, the method provides theoretical guidance for the application of MLDOE in multi-band and wide-band systems. According to the method, an MLDOE suitable for a medium wave infrared (MWIR) of 3.7-4.8 μm and a long wave infrared (LWIR) of 7.7-9.5 μm is designed, and a 10× hybrid zoom lens is designed using the diffraction element for the dual-band. The results show that the modulation transfer function (MTF) of the system at the Nyquist frequency of the MWIR is greater than 0.52 and the MTF at the Nyquist frequency of the LWIR is greater than 0.35.