Abstract: The optimization of the substation secondary system has completed the overall improvement of the secondary system from the technical architecture to the functional design. The reliable operation of the relay protection, the core business of the secondary system, is the key basis for the safe and stable operation of the power grid. In order to fully assess and verify the reliability of the new generation relay protection system, this paper first analyzes the innovation points of the relay protection technology and the resulting operation risks from the aspects of autonomous control, function optimization, operation monitoring and safety enhancement on the premise of the comprehensive optimization of substation secondary system. Moreover, on the basis of sorting out the interactive data flow of the relay protection functions, the key technologies of the relay protection system-level testing are discussed. Test methods for the relay protection in terms of the operation performance under the complex working conditions, the configuration control, the functional interaction and the virtual loop reliability are proposed. In the end, a relay protection system-level test platform is established, accompolishing the comprehensive assessment and verification of the relay protection action performance and function, which is of great significance for eliminating the equipment defects, reducing the peration risks and accelerating the practical process of the optimization scheme.