The invention provides a method and a device for evaluating effect of an over-area power transmission project to atmosphere haze. The method comprises the steps of distributing electric power which is input from over-area ultrahigh-voltage to each power supply point in a receiving-end area according to each power supply point set capacity of a receiving-end area as a virtual power supply point; distributing the electric energy which is supplied from over-area ultrahigh-voltage to a remote power supply point according to the set capacity of the remote power supply point; respectively determining a discharging list of the remote power supply point and the discharging list of the virtual power supply points according to basic information of the virtual power supply points and the remote power supply point, wherein the basic information comprises power generator set capacity of the power supply point, boiler type, fire coal chemical component data and an operation parameter of flue gas treatment equipment; and calculating a model generation evaluation result according to the discharging list of the remote power supply points, the discharging list of the virtual power supply points and the effect of atmosphere haze. The method and the device settle a problem of evaluating effect of an ultrahigh-voltage power transmission project to the atmosphere haze, and furthermore are suitable for the ultrahigh-voltage projects with different types, different capabilities and different areas.