The present invention relates to a GIS corona discharge degree determination method, and belongs to the test dielectric strength or breakdown voltage technology field. The method comprises the steps: 1) installing an ultrasonic sensor configured to monitor GIS corona discharge signals on the GIS; 2) regulating fault factors and voltage grades, collecting corresponding corona discharge signals, and obtaining a plurality of discharge maps according to the corona discharge signals; 3) selecting a reference map from a plurality of discharge maps obtained from the step 2); 4) determining the sound pulse threshold value of the GIS discharge serious degree according to the mutational sites of the sound pulse to the time curve in the reference map; and 5) performing the determination of the discharge serious degree of the GIS in the work state according to the threshold value. The GIS corona discharge degree determination method is provided, a mode for selection of the threshold value through adoption of the reference map is also provided, and a threshold value capable of taking as the basis is provided so as to give out accurate basis for the determination for the fault grade.