High-voltage gas insulate switchgear(GIS) shell circulation is the main cause of operating losses in substations. Circulation can cause the device to heat up. If the substation is operated for a long time, the transmission capacity of the power system and the insulation performance of the equipment will be seriously affected. The purpose of this article is to simplify the loss calculation procedure and improve the calculation accuracy of GIS shell circulation and the efficiency of engineering designers and on-site operation and maintenance. The basic theory of high current bus and engineering electromagnetic field is applied. Based on the principle of hollow current transformers, an equivalent model of GIS shell circulation is established. For steady-state operation of 550 kV GIS and short-circuit fault conditions, circulating currents of shells, short wiring, and grounding wires at different locations are calculated. The circulation and loss distribution rules are given. The calculation results show that when the 550 kV GIS is in steady-state operation, the short-circuit circulating current value at the inlet and outlet ends is greater than other locations; the current value at the fault point near the ground wire is the largest in the fault state; the calculated current of the ground wire and the short wire is greater than the measured value, mainly it is caused by the distribution of grounding resistance. The total loss of GIS system is given through calculation, which gives theoretical guidance for the actual operation of GIS.