The invention relates to a conversion joint for a GIS cable terminal test. The conversion joint comprises a high-voltage test lead and a variable-diameter lead screw, wherein the two ends of the high-voltage test lead are a GIS end and a vehicle end respectively; the GIS end is in threaded connection with the variable-diameter lead screw; the diameter of one end of the variable-diameter lead screwis matched with that of a threaded hole in the GIS end of the high-voltage test lead, and the diameter of the other end of the variable-diameter lead screw is matched with that of a bolt hole in thegrounding end of a GIS grounding knife switch. By applying the conversion joint, the test efficiency can be greatly improved, and meanwhile, the accuracy of fault positioning is improved.