Spatial heterodyne spectroscopy(SHS)is a novel method for hyper-spectral analysis, and instrument line shape function is one of the basic performance parameters, which should be precisely characterized. Based on the analysis of the influence factors(apodization, limited angle, abaxial detector element ) and special requirement for measuring method and source, the present paper put forward a new method for measuring with tunable monochromatic light source, and designed experimental equipment with tunable laser and integrating sphere eliminating speckle. Selecting typical spectral range within band range for high spectral resolution scanning (0.1nm step), the energy distribution of spectrum was obtained according to error correction, spectral reconstruction and normalization .In addition, rule curve for FWHM and wavelength was obtained by the full spectral range scanning interferogram. Finally, theoretical spectrum, ILS convolution simulated spectrum(LBL calculated), and measured carbon dioxide absorption spectrum by ground-based experiment are in good agreement .The result shows that the instrument line shape function exhibits high accuracy.