GIS loop test system and method based on three-phase injection method

The invention relates to a GIS loop test system based on a three-phase injection method. The GIS loop test system comprises an outgoing line sleeve, special line resistors, a switch, automatic change-over switches and a power supply, wherein the outgoing line sleeve comprises an A-phase outgoing line sleeve, a B-phase outgoing line sleeve and a C-phase outgoing line sleeve, the special line resistor is arranged between every two adjacent outgoing line sleeves, any outgoing line sleeve is electrically connected with one end of the switch, the other end of the switch is provided with a current switching contact and a voltage switching contact, and the automatic change-over switch is connected with any two current switching contacts and any two voltage switching contacts to form a test loop.The A-phase outgoing line sleeve, the B-phase outgoing line sleeve and the C-phase outgoing line sleeve are connected with the switch; the special line resistor is arranged between every two adjacentoutgoing line sleeves, the