Insulating parts are easily subjected to pollution which may cause damage to the electric system. A typical disc insulator is chosen as the target to test its flashover voltage by using an artificial pollution system. This test system aims at obtaining characteristic parameters of damage for chosen conducting sols to the selected insulator. Experimental results show that thickness and electric conductivity of pollutant layer over insulators are the main parameters in damage evaluation. The flashover voltage decreases with increase of thickness and/or conductivity. These results provide a better basis on further revealing the damaging nature of conducting sol materials.