The invention discloses an electrified railway traction power supply scheme optimization design method. The number and positions of a traction substation, a section post, an AT post, an opening and closing post and other power supply facilities and the capacity of a traction transformer are set as optimization variables, constraint conditions are set according to the design performance and requirements, an optimization objective function (such as the whole-line minimum power supply capacity (Ssub), the minimum average power consumption (Ploss), the minimum project cost (M), and the like) is determined, and an electrified railway traction power supply system design mathematical model conforming to optimal objective or multi-objective satisfactory optimization is established. All possible traction power supply schemes are automatically compared and selected in the limited domain of the constraint conditions by an intelligent optimization algorithm to determine an optimal or satisfactory scheme conforming to the optimization objective. By adopting the method of the invention, the number and positions of traction power supply facilities, the transformer capacity and other design parameters can be determined automatically, efficiently and accurately, the level of refinement of traction power supply design can be improved, and the traction power supply system construction and operation costs can be reduced.