In this paper, to understand the effect of forest fires on polymer insulators for transmission lines, it was observed the aging of the housing surface of the polymer insulators. And, this paper shows the way how to create the artificial field testing in order to simulate forest fire. As the results of, maximum leakage current peaks by influence of flame increased from 1[mA] to 1.4[mA], and SEM results show the inorganic component on the housing surface because the organic component matters disappeared. Therefore, the case of exposed by forest fire, polymer insulator can be used in the early stage, but an exchange needs active countermeasure to be stabilize power delivery.