Abstract: For the voltage loss of chain type series supply substation, the regional standby automatic switching technology is widely used to restore the power supply. However, the current regional standby automatic switching control algorithm is complex, which is only suitable for EMS systems equipped with large and medium-sized servers. The county dispatching is generally the dispatching automation system of SCADA module. Therefore, the current regional standby automatic switching technology cannot be popularized and applied in County dispatching. According to the reality of county dispatching equipment and the principle of "simplicity, practicality, safety and reliability", a regional standby automatic switching control algorithm is studied. To improve the power supply reliability of county-level power grid. Reduce the voltage loss risk of chain supply substation.