The invention discloses an optimal power network planning method based on a reliability contract. The optimal power network planning method based on the reliability contract comprises the following steps that first, influence factors in the reliability contract are determined; second, an optimized objective function and constraint conditions are defined; third, a power network model capable of being used for simulation calculation is built according to the calculation requirement, and parameters for simulation calculation are determined; fourth, a genetic algorithm is used for solving the optimal planning scheme, meeting the constraint conditions, for the objective function. By the adoption of the optimal power network planning method based on the reliability contract, reliability and economy are closely combined, balance is achieved between increased equipment investment and reduced power failure compensation cost, the overall benefit is maximized, and the reference basis is provided for decision making of an electric power system planning scheme.