Imaging spectrometer uses a space-borne diffuser to obtain solar reference spectrum. The spectral features of space-borne diffuser will be introduced to the solar reference spectrum. The spectral features that interferes the gas absorption structure influence the inversion precision of gases. The causes of spectral structure of aluminum diffuser is analyzed, and the spectral structures in the observation angle [15 degrees, 40 degrees] are measured in laboratory. The results show that the spectral structuse increases with wavelength: 450 similar to 600 nm, the spectral structure is 0. 2%similar to 0. 6%; 600 similar to 750 nm, the spectral structure is 0. 3%similar to 1. 6%. Spectral structure reduction method is discussed. The spectral structure can be reduced about 76% by smoothing the spectrum of aluminum diffuser.