The invention discloses an optimal maintenance decision method of power transmission and transformation equipment based on a Markov decision process. The method comprises that a state transfer relation diagram, of transfer relation among different states, of the power transmission and transformation equipment is established; a state maintenance model of the power transmission and transformation equipment is established according to the state transfer relation diagram of the power transmission and transformation equipment; the Markov decision process is used to solve the stable-state probabilities of different states of the power transmission and transformation equipment; a function relation between a maintenance strategy and pay corresponding to the maintenance strategy is established; a Markov based maintenance decision model of the power transmission and transformation equipment is established by taking maximization of certain function value of a pay sequence in the maintenance strategy as a sequence decision problem; and according to the stable-state probabilities of the different states of the power transmission and transformation equipment, a strategy iteration method is used to obtain an optimal maintenance strategy by solving. The method has the advantages that the Markov decision is used to make compromise between the maintenance cost and fault loss, the optimal maintenance decision is obtained, and reference is provided for maintenance deciding staff.