Abstract: In recent years, the insulator pollution in expansive soil areas is relatively severe. Taking a 500 kV double-circuit line in the expansive soil area of Baise, Guangxi as an example, based on the extraction,test and analysis of the insulator pollution, it is found that the high pollution rate and poor cleanliness of the glass insulator in the expansive soil area are caused by the fine particles of montmorillonite, one of mineral components of the expansive soil, adhering to the interior of glass insulator umbrella skirts under long-lasting wind circumstances, and thus several preventive countermeasures are put forward.