Current transformer magnetic saturation margin is a calibration item in JJG1021《electric transformer》,the paper puts forward a new type of current transformer magnetic saturation margin direct measuring method based on ratio converter, with this method introduces a current transformer 2 times magnetic saturation margin measurement device, solves the overflow and overload problems of standard current transformer, current load case and transformer verification, the device can ensure that current transformer 2 times magnetic saturation margin measurement has tranceable and transferable measurement attributes