With the enlarging scale of power grids, the quantity of electric equipments is increasing and their quality is improving. Therefore, the optimizing management of equipments, which is an important act to reduce investment and increase economic benefit of power grids, has been paid more and more attention. This paper makes a comprehensive analysis of factors that influence the life cycle cost of electric equipments. Considering the risk of power grid caused by the fault of equipments and other relevant factors, the economic life model is established and the judgment about the optimal maintenance strategy is proposed. The proposed maintenance strategy is conducive to save the operating cost of power grids and optimize the investment. Also, it can promote the refined management and provide reference decisions for electric utilities to plan and adjust equipments operating better.