Abstract: The paper discusses a zero-flux current transformer technology, and applies it to stability tests of the large current, which may used to test the current stability of the CM2 program-controlled current stable supply, in a range up to 10-5/8h. The discussion includes the fundamental principles of the zero-flux current transformer technology, automatic measurement methods for the current stability of the CM2 current stable supply, an analysis of the impact of the high current stability in the on-site testing and the related solutions.