Abstract: Under the study of condition-based maintenance for power transmission system（CBM-PTS）,the model and solution of condition-based maintenance for substation（CBM-S） was studied.The equipment involved in this paper were only associated with the substation from the view of the topology.The necessity of the research for CBM-S was discussed first,and the equipment condition in the research time was obtained by Markov process under the technique of state monitoring and forecasting.Furthermore,the quantitative expression of the failure risk and maintenance risk were provided,in which the maintenance time was the only parameter.Then,the decision-making model of CBM-S was established.The goal of the model was to minimize the sum of failure risk and maintenance risk,and the maintenance constraints were also considered in this model.The genetic algorithm was selected to solve the model.The analysis of simple example demonstrates the necessity and effectiveness of the study.This paper is the further study of the CBM-PTS,and is an important part of the decomposition and coordination of the decision-making process for CBM-PTS.