Normally, describing for the behavior of remanence of CT saturated core under exposure of operating currents is often based on assumptions and simulations. Due to the remanence have a large influence for CT’s behavior especially for protection CT, so it is not exactly to do the protection analysis with assumptions for the behavior of remanence. Therefore some testing had been performed with new test method to get the residual magnetism, unexpected, there have a large difference between the research result and the assumptions for the behavior of remanence. Therefore, accident analyse of electric grid will benefit from this research result.