The imaging spectrometer, which uses a multi-zone grating as the dispersing element, can realize the sharing of optical elements. It has the advantages of wide wavelength band, high spectral resolution, and compact structure. However, the stop of this system is located at the multi-zone grating and the broadband beam is incident on the whole grating area of each channel at the same time. The multi-order diffraction of the gratings with different frequencies will cause interference among different channels, and thus it is difficult to be removed by the order-sorting filter. This problem seriously influences the extraction and analysis of the effective spectral signals, and even overwhelms the effective target signals. This paper uses ray tracing to determine the source of multi-order diffraction stray light in the system, and calculates the diffraction stray light coefficient with the analysis model. According to the structure of the optical system, two methods for suppressing the multi-order diffraction stray light using the linear variable filter and the stop coating are proposed, and the bandwidth requirement of the filter and the improvement effect of diffraction stray light coefficients using the stop coating are analyzed. The analysis results show that the stop coating method can reduce the diffraction stray light coefficient to 0.57%. Compared with the linear variable filter method, the stop coating method is easier to implement, and is more preferred for the suppression of multi-order diffracted stray light in the imaging spectrometer with multi-zone grating.