The image quality of the grating spectrometer is often affected by the polarization characteristics of the incident light. In order to solve this problem, a depolarizer is usually added to the spectrometer to reduce the polarization response of the instrument. The birefringence property of the crystalline material can produce a depolarization effect on the optical principle, therefore it is often used to process into various types of depolarizers. Based on the principle of the matrix optics, the Muller matrix and residual polarization theoretical expression of a H-V depolarizer and a double Barbinet depolarizer were deeply discussed. The relationship among residual polarization of a double Barbinet depolarizer and working wavelength, its wedge angle, entrance pupil diameter and incident light polarization angle was given respectively. Based on these theories, a double Barbinet depolarizer applied for a grating spectrometer was developed. It could be obtained by calculation that when the wedge angle and the pupil diameter of the double Barbinet depolarizer was 0.6° and 20.6 mm respectively, the residual polarization of the depolarizer was better than 3% in the wavelength range of 0.4-0.9 μm. What’s more, the double image distance met the application requirements, so it can be widely used in engineering practice.