Abstract: The fine structures of traditional calibration sources and target spectra may have differences, which could hinder the calibration accuracy of hyperspectral remote sensors. Furthermore, traditional sources are difficult to be measured accurately. To solve such problems, a novel spectrally tunable source based on digital micromirror device (DMD) and spectroradiometer structure was introduced. The optical system of the new source was designed. The principles of the system, structural parameter calculation of the system and the process of optical design were described in detail. The results indicate that the optical system's performances are near-diffractive-limit in the whole band from 0.4 m to 1.0m. The RMS spot radii are less than 3.5 m and the MTFs at 37 lp/mm are near 0.8 for all the design wavelengths, which meet the requirements of the source.The novel source is promising to improve the imitation accuracy of target spectra, and it could also be measured accurately by detector-based calibration method. With these features, the new source is helpful to reduce the calibration uncertainties of remote sensors.