Abstract: The timely and accurate online estimation for composite insulators of transmission lines can effectively prevent pollution flashover accidents. A visualized estimation method of composite insulator pollution status of transmission line was proposed in this paper. Firstly, a semi-automatic registration method for multisource reflective spectral images was constructed by combining image registration algorithm and target area selection, which solved the inherent image registration problem of multi-lens camera. Secondly, model pre-training was conducted through shooting artificial contaminated samples using the low cost, lightweight, and high imaging quality multi-lens multispectral imaging equipment, and further transfer training was conducted through real natural contaminated samples to construct a pollution grade diagnosis model of composite insulation material surfaces. Finally, the actual pollution status of transmission line composite insulators was measured and analyzed under different shooting conditions using the unmanned aerial vehicle platform. The results indicate that the pollution grade classification accuracy for artificial and natural contaminated samples is 95.3% and 87.8%, respectively, and the pollution grade classification accuracy for actual transmission line composite insulators can reach up to 90% with pollution distribution area clearly displayed. The feasibility of transmission line insulator pollution grade estimation and pollution distribution visualization diagnosis based on reflective multispectral imaging technology is verified, which can provide a new technique for status inspection and maintenance decision of transmission line insulators.