With the ongoing construction and continuous improvement of China’s ultra-high voltage transmission project, the utilization of eight split conductor is increasingly prevalent. However, the presence of icing presents a significant risk to its secure and dependable operation. Undertaking research on the growth model of icing on transmission lines holds paramount significance in bolstering the power grid’s capacity to effectively mitigate ice-related disasters. Nevertheless, there has been a scarcity of studies focused on modeling the growth of icing on eight-split conductors, and the impact of high voltage on icing growth has not been taken into account. This paper establishes a comprehensive numerical model for determining the equivalent icing thickness of transmission lines under integrated load conditions. The model is developed through a meticulous analysis of arc sag variations and temperature measurements. A comprehensive conductor charged icing test is conducted in a natural environment in this study, utilizing the resources of the Xuefeng Mountain Energy Equipment Safety National Observation and Research Station of Chongqing University. The objective of the study is to analyze the growth characteristics of the icing, measure the fluctuations in arc sag for the split conductor, and validate the accuracy of the developed numerical model. The results revealed that in a natural icing environment, the icing thickness of eight split conductors exhibits a non-linear increase with the passage of time. When a conductor is lightly covered with freezing fog, the roughness of the icing significantly increases due to the influence of the electric field. Consequently, the icing becomes more loosely packed, leading to a lower density. The model’s theoretical calculation values for the equivalent icing thickness exhibit a maximum relative error of 10.7% when compared to the corresponding measured values.