The numerical simulation method can provide a more detailed analysis of the spatial electric field distortion during guano flashover faults, and is easy to analyse the impact of parameter changes on the results over a larger range. It can simulate and analyse the actual guano flashover characteristics of the transmission line, which helps to analyse the dangerous areas that cause air gap breakdown in the presence of guano, and thus determine the protective range of bird protection measures. Based on this, a practical transmission line model is established to analyse the potential distribution near typical tower insulator strings of transmission lines under the condition of guano. Based on the average electric field intensity data of gap discharge, the influence of the horizontal distance between guano and insulator strings on gap discharge is analysed, and the dangerous area of air gap breakdown near insulator strings during guano is drawn.