The establishment of failure risk assessment on the secondary system in smart substation can help power gird company timely arrange maintenance when the failure risk of equipment accumulates to a certain extent,thus effectively preventing systematic failure. In this paper,a probabilistic failure model is established through Weibull probability distribution function from a perspective of reliability engineering. According to the type tests and various daily operation statistics of secondary equipment,the regression equation calculated by the average rank method and least square estimation can obtain the model parameter estimation. By doing so,the equipment failure model close to the real operation condition can be obtained. Moreover,the relationship between the failures of the secondary system and a single equipment is established through the fault tree. Therefore,the risk probability distribution function of top event in secondary system can be calculated quantitatively,which can provide auxiliary decision for risk warning and state overhaul. Finally,it is verified by the numerical results that the proposed secondary equipment failure model can provide a reference for accurate time arrangement for system maintenance.