Short time over current effect experiment is significant on testing electrical device’s capability of tolerating instantaneous large current, and both on calibrating smart meter’s working performance. Our paper propose a novel approach of calibrating the short time over current experiment approach by using current clamp and digital oscilloscope, and describe the method of evaluating measurement uncertainly. This approach, which the calibration precision and uniformity are confirmed through result comparison, can provide important technology base for short time over current effect experiment.