Abstract: There is more pollution data for standard porcelain or glass insulator of UHVDC transmission lines but relatively less data for composite insulators. Most of them are not charged, which can not accurately obtain the comprehensive influence of electric field force, wind force, gravity, and other comprehensive effects on pollution accumulation characteristics of composite insulators during operation. In view of these existing problems, taking ±800 kV UHVDC transmission line as an example, this paper conducts a simulation analysis on the contamination accumulation characte-ristics of the operating composite insulators, and the substantial pollution degree of the composite insulators is measured and verified during the comprehensive inspection of the transmission line. The results show that the deposition of polluted particles on the surface of charged composite insulators results from the combined action of air drag force, gravity, and electric field force. The increase of the charged polluted particles and the enhancement of the electric field force has a more significant effect on the particle motion process, that is, the smaller the atmospheric wind force, the more obvious the effect of the electric field force on pollution accumulation. The equivalent salt deposit density of the umbrella skirt at the high-voltage end of the composite insulator on the UHVDC transmission line is higher than that at the middle and low-voltage ends. The whole string is distributed in a “U” shape, consistent with the distribution rule of the electric field along the string of charged composite insulators.