In order to achieve the management and control of smart substation operations, this paper proposes an impact range positioning method based on upgrading SCD in modification or extension project. According to comparing primary system specification description part in SCD file, the scope of influenced bays can be located. Then, it is judged whether the secondary device is affected or not by comparing IED’s CRC. To compare the affected IEDs’ communication description part and input description part, the influence scope of secondary system of physical link circuit and logical link circuit before and after modification and extension can be located respectively fast. At last, it provides the graphically modeling tools to realize this effective means of positioning the influence scope in secondary circuit by upgrading SCD.