Insulators pollution flashover is a major reason affecting the safety and stability of power grid. Pollution is the premise of flashover, transmission lines in different regions are located in different environments, resulting in different pollution accumulation characteristics. So it is necessary to analyze the natural pollution accumulation of transmission lines in the study area. In this paper, the pollution samples of 500kV line insulators in a certain area are studied from Equivalent Salt Deposit Density (ESDD), Non-Soluble Deposit Density (NSDD), NSDD/ESDD ratio, pollution ratio, pollution components by statistical method. The statistical results show that the whole sample lines are in the light pollution level, and the average values of ESDD, NSDD, NSDD/ESDD ratio and pollution ratio are 0.0096mg/cm2, 0.0076mg/cm2, 7.9 and 1.29, respectively. The pollution composition of insulators is related to the local environment where the transmission line is located. Based on this, the precise anti-pollution measures of the transmission line are put forward.