The main portion of the space-borne grating imaging spectrometer-grating has intense polarization response. The objective of spectrometer is to measure the intensity accurately without bias as to the incident polarization state. One common method to overcome polarization bias in optical systems is the insertion of a depolarizer. The theory of horizontal-vertical (H-V) quartz depolarizer operation is described. A single H-V depolarizer was met the spectrometer polarization requirement according to its polarization character. Both the degree of depolarization and image degradation (especially the image doubling) were analyzed for the depolarizer design. The analysis results show that it satisfies the design requirements of the spectrometer, the polarization sensitivity is within the specification of 1% and the decrease in MTF due to the depolarizer is less than 1.5%.