In order to achieve the optimized energy allocation, long-distance and high-capacity transmission is becoming more common in the novelpower system. This requires insulators to operate in a wider geographical area, crossing different climates and geographical environments, thereby increasing the opportunities to come into contact with various sources of pollution. At present, the flashover problem of composite insulators in heavily polluted environments in special areas under the novel power systemhas not been solved. However, the existing pollution flashover models mainly target conventional pollution levels, and there is no flashover model for insulators under heavy pollution conditions. Accurate flashover models are the key to insulation configuration and pollution flashover warnings under heavy pollution conditions. To this end, this paperwill study and propose a flashover model for composite insulators in extreme environments of the novel power system. Firstly, this paper puts forward an approach to work out the flashover voltage of composite insulators in the context of heavy pollution, introducing the concept of random arc, which is more in line with the arc development state under heavy pollution conditions; Deriving the residual fouling layer based on the electric axis method in electromagnetic field theory is more suitable for multi-arc states; And the key model parameters under heavy pollution conditionsare tested and corrected. The final experimental verification shows that taking the pollution level of 0.4mg/cm2 as an example, AC pollution flashover voltage gradient test value of the composite insulators is 31.6 kV/m, and the model calculation value is 30.0 kV/m. The calculation error and error percentage are only 1.6 kV/m and 5.06%, respectively. The maximum error percentage in calculating the AC pollution flashover voltage gradient within the 0.4 mg/cm2~1.2 mg/cm2 range is less than 10%. The calculation method proposed in this paper is highly accurate. The research results of the paper supplement the pollution flashover model under conventional pollution levels, which has important reference significance for insulation configuration and pollution flashover warning under high pollution conditions.