Abstract: In order to solve the problem of optimal maintenance strategy for existing aseismatic structure, on the basis of Markov theory and comprehensively considering such factors as the damage degree of structure, maintenance expense, etc., the authors establish a mathematic model determining the optimal maintenance strategy with the minimum maintenance expense as the target function. The state of aseismatic structure can be divided into five sorts. The corresponding maintenance strategy is also classified as 'single state', 'two states' and 'three states'. According to the current state of structure, the state transition probability matrix can be analyzed. Through resolving the minimum maintenance expense of aseismatic structure, its optimal maintenance strategy can be analyzed. In the decision of maintenance, it is unreasonable only to consider 'single state'. Different maintenance strategy should be adopted according to different states.