Abstract: In order to realize the fast control of controllable self recovery energy release device used in Baihetan Jiangsu ±800kV Ultra High Voltage (UHV) Hybrid DC transmission project, a novel plasma jet triggered SF₆ gap switch prototype with high air pressure and large trigger energy is developed. The trigger cavity of the gap switch adopts a two-stage surface discharge structure, which can realize fast and reliable triggering within 1ms under extremely low working coefficient. In order to improve the trigger life of SF₆ gap switch, a test platform was built and the experimental research was carried out. Firstly, the influence of the structure size of the trigger cavity on the life of the SF₆ gap switch is studied. The results show that increasing the surface distance of the first stage trigger cavity can effectively improve the trigger life, but the cavity should not be too long, otherwise it will cause arc extinction. So the size of the trigger cavity is 3.5mm + 6mm. Then, the influence of the trigger chamber material on the trigger life is studied. The results show that the gas production capacity and ablation resistance of polytetrafluoroethylene (PTFE) are relatively balance. The comprehensive performance of PTFE is better than that of polytetrafluoroethylene with molybdenum disulfide or boron nitride, which can effectively increase the trigger life to 583 times. The research shows that the deterioration of the trigger cavity is the fundamental reason for the end of the trigger life of SF₆ gap switch. In this paper, a monitoring method of the deterioration process of the trigger cavity is proposed. The variation of some characteristic parameters with trigger times can be used to monitor the deterioration process of the trigger cavity, such as the surface flashover voltage of the primary cavity, the residual voltage of the energy storage capacitor when the secondary cavity is on, the conduction delay of the secondary cavity and the conduction delay of the main gap, so as to monitor the state of the trigger cavity and improve the reliability. Through the above research, the trigger life of SF₆ gap switch prototype has reached up to 583 times, which meets the engineering requirements, and the SF₆ gap switch has the function of trigger cavity state monitoring, which improves the reliability.