In this paper, the effect of the relative microstructure heights error on the diffraction efficiency of multilayer diffractive
optical elements (MLDOEs) is considered. Based on the relationship of diffraction efficiency and diffractive
microstructure height, the analysis result of the relative microstructure height error on the diffraction efficiency of
MLDOEs for 8-14μm far infrared optical system was present. It is shown that the diffraction efficiency over the whole
waveband is above 98.94% for double-layer DOEs when the two relative microstructure heights error are equal and both
controlled within ±2%. However, the diffraction efficiency drops quickly when the two relative microstructure heights
error changed in the opposite sign. The analysis result can be used for analyzing the effects of microstructure heights
error on diffraction efficiency for MLDOEs working in infrared optical system.