The grating dispersive imaging spectrometer is used for ocean color remote sensing. It is operated in the visible and near infrared range. A push-broom method is applied to the instrument. 15 spectral channels and 1024 cross-track pixels comprising a total field of view of 14.2° are arranged on the focal plane. The spectral channels are sensitive to the polarization of the incident light. To improve the radiation measurement precision at the top of atmosphere, it is necessary to understand the polarization response characteristics of the instrument, including the polarization sensitivity and the phase angle. A polarization testing system is established before launching. The polarization sensitivity and the phase angle data of all spectral channels, which vary with the channel No. and the cross-track pixel, are measured. The 980 nm band has the highest polarization sensitivity and its mean of the cross-track pixels is about 4.69%, while the 443 nm band has the lowest sensitivity with a mean of about 1.81%. The sensitivity of middle field of view is lower than that at the edges in the same channel. A polarization response correction method is proposed for the imaging spectrometer. Verification experiments are performed by introducing the partially polarized light with a known polarization state. The result shows that the radiometric uncertainty caused by polarization response of the instrument can be reduced by 1%-6%.