Hadamard transform optics has been developed in the past decades. It has been used in distinguishing targets, detecting feeble signals and so on. Hadamard transform spectral imager (HTSI), based on Digital Micro-Mirror Device, is a new dispersion spectral imager. HTSI has been developed in our laboratory. The spectral heterogeneity of encoded image captured by HTSI has been researched according to spectrum calibration in this paper. Relative and absolute spectrum emittance calibration algorithms have been proposed first time on HTSI to meliorate the spectrum heterogeneity. It aims at the problem that the accuracy of recovered spectrum is depressed by the heterogeneity noise and disorder encoding spectrum in spectral image. Simulation and experiment result have demonstrated that the meliorated spectral curve is close to the standard spectrum, and the variance of the recovered spectrum ranges from 2.4% to 4.2% with regard to the spectral image of 7 waves. This is fully satisfied for the requirement of laboratory and projects.