with the development of optical technology, optical instruments become smaller and more integrated. because of the high diffraction efficiency and light weight, binary optical elements become more and more popular. binary optical element can only blaze at one wavelength, it has high diffraction efficiency at design wavelength. but the diffraction efficiency of binary optical elements will decrease quickly with the change of wavelength. and this situation will have big impact on image quality. since double-layer boe can blaze at two wavelengths, it has high diffraction efficiency at wide spectral bandwidth. there are kinds of fabrication errors. based on scalar diffraction theory, this paper analyzes the diffraction efficiency of double-layer boe with fabrication errors and simulates it in matlab. simulation shows the diffraction efficiency decreases quickly if the depth errors of two layers are opposite, and this situation should avoid. as for periodic errors, tilt errors and angular errors, these fabrication errors have different impact of double-layer boe on diffraction efficiency.