Abstract: Due to the extreme operating conditions of superconducting cable terminal, the insulation material is subjected to high electric fields with a maximum temperature gradient of nearly 100 K. The operating conditions of terminal insulation material GFRP (Glass Fiber Reinforced Plastic) are taken into account, and the surface charge accumulation characteristics under temperature gradient and its influence on the surface flashover voltage are studied. Firstly, the surface flashover voltage of GFRP under different temperature gradients is measured. Secondly, the simulation model of charge transfer model in gas-solid interface is established, and the charge accumulation characteristics under the different temperature conditions is calculated as well as the distortion of electric field. Results show that temperature gradient will significantly reduce the surface flashover voltage. When the temperature gradient is 100 K, the partial discharge initial voltage and flashover voltage are only 74.0% and 75.9% of that without temperature gradient, respectively. Furthermore, the surface electric field can increase nearly 10 times owing to the surface charge accumulation, as suggested by stimulation results. Therefore, the surface charge accumulation under the temperature gradient is responsible for the decrease of surface flashover strength. This research is helpful to understand the characteristic of charge accumulation and its effect on flashover voltage under temperature gradient, and is of great significance to insulation optimization design of low temperature dielectric insulation.