The invention discloses an atmospheric pollutant granularity based power transmission line path selection method, which comprises the steps of acquiring meteorological data of a region by which a power transmission line is planned to pass, and classifying dominant wind directions in different seasons; performing particulate matter collection on the region by which the power transmission line is planned to pass in a segmentation manner; performing granularity analysis on particulate matters in different segments under different dominant wind directions; coating a fixed amount of simulated dirty on a certain area of the surface f a composite insulator, and detecting the hydrophobicity and hydrophobic mobility; performing a flashover test on a test object to acquire flashover voltage; and selecting the granularity with high hydrophobicity and high dirty flashover voltage, and regarding a segment with the granularity to be a recommended path passing region. The power transmission line path selection method has the beneficial effects that the pollution severity of a line path can be evaluated comprehensively, the risk of pollution flashover is reduced, and the line running reliability is improved.