The invention relates to a method for determining the pollution grade change of a power grid theory. The method comprises the following steps: determining the air quality index P of power grid pollution area flashover features; determining an ESDD (Equivalent Salt Deposit Density); and reckoning a pollution grade change situation of the power grid theory in real time. The method considers that atmospheric pollutants in each area have certain difference and the influence degrees of SO2, NO2 and PM10 in the atmospheric pollutants in each area can not be identical, the method makes correction suggestions for an empirical formula, which is given by certain scientific research institution, between a salt density value and an atmospheric quality index, and main pollutant PM2.5 in the atmospheric pollution in recent years are brought into the empirical formula. An atmospheric environment parameter independent term including PM2.5 is established, an independent term selection method and principle are put forward to obtain the method for determining the pollution grade change of the power grid theory by the atmospheric environment parameters including PM2.5 and the like in real time.