Abstract: In application of high voltage and large current discharge, thyristor series is widely used as main switch of discharge circuit. If the thyristor conducts slowly, a large number of Joule heat will be produced in chip which leads the thyristor damaged. When thyristors are working in series mode, if the conduction time of thyristors are not consistent, the slower conduction thyristor will be subject to high voltage and breakdown, so the thyristor series must be triggered fast and synchronously. For the above problems, an indirect and strong trigger circuit of thyristor for high voltage and large current pulse discharge was proposed. The circuit uses indirect light trigger method, and in the trigger circuit, trigger signals of thyristor series are controlled by the same control signal through the optical fiber, strong trigger pulse current is produced after photoelectric conversion, so as to realize fast and reliable conduction and synchronization for thyristors. The experimental results show that the circuit can realize reliable trigger of thyristor series, trigger pulse width time is adjustable, and discharge voltage is 9 kV and discharge current is up to 32 kA, which meets application requirement of pulse discharge power supply module.