Abstract: A tri-electrode self-steepening switch was researched. Then a triggering system was designed with a transformer driver and the self-steepening switch to satisfy the requirements of the trigatron. Statistical analysis on steepening parameters of the switch was conducted under multiple driving modes to reach the optimized self-steepening mode. The optimization combination of switching polarity, working electric field, UV radiation intensity and time were determined. The switching possibility of the trigatron was obviously improved when the self-steepening segment was inserted. Meanwhile, the delay and the jitter of the trigatron decreased significantly, and its working voltage-ratio range was broadened.