Spatial heterodyne spectroscopy (SHS) is a new spectrometric technique. Based on the basic concept and characteristics of spatial heterodyne spectrometer, an interferogram correction method is presented for the signal from both interferometer arms. The interferograms from unequal arms of interferometer were calculated and corrected by use of the presented method, and the corrected interferogram is very close to the ideal SHS interferogram. The main idea is to measure the nonmodulated term (the signal intensity of each arm) of the interferogram and introduce a correcting factor in the interferogram data processing. The spectral inversion accuracy of spatial heterodyne spectrometer can be effectively improved by correcting the interferogram aberration caused by unequal interferometer arms.