The switch rate of thyratron is related to the triggering signal. The fast thyristor is usually used in the trigger circuit, but the triggering signal is not ideal. This paper brings forward a new method of substituting power MOSFET whose switch time is shorter for thyristor in developing the pulsed fast discharge power supply of sulfur dimmer. The Experiment results prove that it can greatly improve the conduction characteristic of thyratron HY3202.