The invention relates to the technical field of the electrified railway, in particular to an electric energy quality evaluation method of an electrified railway accessed power system. The electric energy quality evaluation method adopts the following technical scheme: (1) the invention aims at obtaining a negative sequence computing method which is suitable for building single-phase load simulation of the electrified railway in power system simulation software (PSD) which is generally used in power systems, and (2) the invention aims at obtaining a method that is used for calculating the current value, which is allowed to be injected in the electrified railway by a point of common coupling, of the harmonic wave at each order in the power system in which the electrified railway traction station is accessed by way of T-type wiring. In the invention, system evaluation simulation calculation is carried out on the related problems of the electric energy quality of the electrified railway, the analysis and evaluation of related problems of the electric energy quality are provided, so as to give guiding suggestions to the design, compensation and fixed value selection and the like of theelectrified railway and the corresponding power supply system.