This paper researched the ageing resistance of glass fiber reinforced polymer (GFRP) in transmission tower under thermal oxidative aging environment. The parameters of the not ageing specimen and the thermal oxidative aging specimen were compared and analyzed, such as tensile strength, elastic modulus, Poissons ratio, and so on. The test results show that the thermal oxidative aging environment has obvious influence on the performance of GFRP material, which significantly reduces the strength of GFRP material, and increases the elastic modulus and the Poissons ratio of GFRP material. And the impact of thermal oxidative aging on the material properties of GFRP material without any protective coatings is more significantly than those with protective coatings. According to the experiential formula of ageing, the working life of specimens with protective coatings are up to 35 years, with taking the half of limited strength as index. Therefore, designers should consider the adverse effect of the external environment and take protective treatments appropriately in the design process of the GFRP transmission tower with the long-term exposure to adverse environment.