Abstract: Relay protection system with long life and high reliability in smart station is different from the traditional protection systemwith respect to the structure,components and working mode,and its life distribution follows different distribution models. Lognormaldistribution model is widely used in the life modeling of electronic products for its flexibility,and has higher adaptability for repairablesystem life. In the process of practical analysis,the lognormal distribution,Weibull distribution and generalized exponential distributionis used interchangeably,resulting in a large deviation in the life expectancy and over-maintenance. The paper establishes a life modelbased on lognormal distribution,uses maximum likelihood function method to discriminate models for censored data,and adopts theleast square method and mean rank order method to give the parameter estimation,then implementing the life evaluation of the relayprotection device in the smart substation. It is verified by examples that the estimated life with the life model is closer to the actualconditions compared with the traditional Weibull distribution.