The highly reliable new generation substations of SGCC have the characteristics of independent controllability, safety and reliability, advanced applicability, and intensive efficiency. They are currently the preferred technical route for smart substation renovation. However, traditional smart substations have significant differences from the new generation substations in terms of network system topology, secondary equipment configuration principles, and message compatibility of the process level. This article proposes the design principles of a secondary information conversion device that realizes compatibility conversion between electrical and digital information interfaces, as well as the implementation process of the new generation substation secondary system renovation. For substations that use various sampling tripping and network schemes, secondary circuit technology schemes and highly reliable network topology structure for the secondary system during the reconstruction are proposed, ensuring the independence of the dual network and the integrity of the data flow. To ensure that a single network anomaly does not affect the normal operation of other networks, the data flow control technology adapted to different network topologies is proposed.