Abstract: Aiming at solving the problem of the complicated tests of the stability of switching power supplies, a non-contact testing method of qualitative analysis for the stability of switching power supplies is presented. Several issues are discussed, including the stable principles of switching power closed-loop model, the coil model, and the radiation signal processing, etc. Coil is utilized to detect magnetic leakage radiation of magnetic elements of switching power, and the stability working information of switching power supplies is achieved via amplifying, transmitting and processing of the radiation signals. The validity of the methodology is verified by experiments.