Risk assessment is an important task of operational management.It is necessary to carry out risk assessment in order to ensure the safe operation of substation secondary system. According to the past researches, the difficulties of its risk assessment include two parts, one is secondary devices are of high quantity and complex relationship, and difficult to consider comprehensively, anotherit is difficult to quantize the impact of secondary devices on primary devices as the main risk. To this end, acombination model of risk transferandnetworktheory is introduced. The risk assessment is decomposed into two parts:one is its own riskassessment which is solved using network theory, another is impact on primary system which is solved using risk transfer model. Then, a set of risk index system is presented according to the needs of different departments. Finally, a real smart substation secondary system is taken as an example to verify the correctness of this method. This work is supported by Technical Transformation Project of State Grid Corporation of China(No.26150515003c).