More and more high-power equipment in the power grid is put into use, and the impact load is increasing. The impact load not only has an impact on the operating status of the power grid, but also leads to an overshoot of the energy metering of the smart electricity meter. This article first analyzes the run-length characteristics of impact current fluctuations in hospital CT machines. Then, establish a system-wide model of the smart electricity meter and a simulation algorithm for energy measurement. Finally, the simulation analysis shows the impact of the impact load of the hospital CT machine on the dynamic error of the smart meter. And through experiments it is verified that the simulation analysis affects the result.