To investigate the fouling characteristics of the composite insulator surface under the salt fog environment, the FXBW-110/120-2 composite insulator was taken as the research object. Based on the field-induced charge mechanism, the multi-physical field coupling software COMSOL was used to numerically simulate the fouling characteristics, explored the calculation method of ESDD, and demonstrated its rationality. Based on this method, the pollution characteristics of the composite insulator under the pollution fog environment were studied, and the influence of wind speed, droplet size, and voltage type on the pollution characteristics of the composite insulator was analyzed. The results showed that: with the increase in wind speed, the amount of accumulated pollution of insulator increases in the range of droplet size, and the relationship between wind speed and accumulated pollution is approximately linear; at the same wind speed, the amount of accumulated pollution increases with the increase of droplet size under the action of DC voltage; when there is no voltage, the amount of dirt on the upper surface of the insulator is more than that on the lower surface, while it is the opposite under DC voltage.