At present, it usually relies on monitoring the surface leakage current of the insulator to realize the flashover warning. As a contact online monitoring method, it still has much room for improvement in terms of reliability and convenience. However, studies have indicated that it can be effectively monitored in a non-contact manner. Therefore, the electric field distribution characteristics of insulator space under typical surface conditions are studied. Firstly, the electrostatic field simulation model of common post insulators is established by using finite element simulation software. The magnitude of the electric field around the insulator under dry, wet and discharge conditions and the law of change are compared and analyzed. Finally, the artificial contamination test is used to verify the simulation results. The results show that the magnitude of the amplitude reflected by the insulator space in different surface states is obvious. Under the condition of surface wetting and arc creepage, the vertical component of the spatial electric field increases by nearly 50% and 20%, respectively. The research results can provide new ideas for condition monitoring of transmission and distribution external insulation.