The invention discloses a quarterly power transmission and transformation integrated maintenance optimization method based on a genetic algorithm, belongs to the field of optimal operation of power systems, and solves the problems of high and unreasonable workload, and the like of a maintenance mode of a power grid. The method comprises the following steps: determining flow sequences of the power grid during the target time period according to quarterly load prediction of the power grid, startup mode arrangement and topological data of the power grid; determining flow sequences of the power grid in a maintenance mode; setting a fault set; checking whether system flow in the maintenance mode meets the thermal stability requirements or not, and working out overload quantity of an overload element; creating a quarterly power transmission and transformation integrated maintenance optimization function of the power grid, and substituting the overload quantity of the element into the function for solving; updating a maintenance mode group by the genetic algorithm, and recombining the flow sequences of the power grid in the maintenance mode; performing loop iteration and calculation to obtain an optimal quarterly power transmission and transformation integrated maintenance scheme of the power grid. Therefore, the working efficiency of power grid operation personnel is improved, the obtained maintenance scheme of the power grid is reasonable and reliable, and the social and economic benefits are remarkable.