As the core component of large-capacity converter valves, thyristors withstand long-term electrical and thermal stress during service. Once the device characteristics degrade and cause systematic failure, it will seriously affect the safe operation of converter valves and even the entire DC transmission project. Therefore, online, accurate, and reliable monitoring research on the health status of thyristors can not only fully utilize the performance and lifespan of devices but also improve the reliability of the entire converter device. This article proposes an online measurement scheme for gate current based on PCB Rogowski coil current sensor, which can be used to monitor and evaluate the aging status of thyristors. Through experimental verification, the gate-triggering current of the thyristor has a good linearity with temperature. Furthermore, an evaluation of the aging degree of the thyristors was completed.