Based on a brief introduction to the current methods of stray light testing and correction, the spectral stray light matrix calibration, which is the core content of the spectral stray light matrix correction method, is introduced in detail in this paper. Then, to calibrate the stray light matrix of the prototype of the forward limb imaging spectrometer, we set up a stray light matrix measuring device in the laboratory. Finally, the accuracy of the stray light correction method based on the stray light matrix of the instrument is verified in an external field experiment.