The application discloses a resistance anomaly detection system for a GIS main loop. The system comprises a power generation detector, a central processing unit and the GIS main loop, wherein the power generator is electrically connected to the central processing unit, the current terminal of the power generator is respectively connected to a first joint and a second joint for outputting current to the GIS main loop, and the voltage terminal of the power generator is respectively connected to the first joint and the second joint for monitoring the voltage of the GIS main loop. The system determines the resistance abnormality of the GIS main loop by monitoring the voltage value of the GIS main loop, calculating the resistance and comparing with the preset alarm threshold, and further determines which switch device or joint has an abnormal condition by detecting the temperature of the GIS shell, the temperature of each switch device and the gas temperature and pressure value in the GIS,and can apply a constant current source that is consistent with the actual load, accurately simulate the actual situation, and reduce the complicated environmental interference on the measurement result.