In High Voltage Direct Current transmission systems, the Thyristor Control Unit plays a pivotal role in managing and overseeing the performance of thyristor modules. This study explores the operational principles of the TCU and the time-domain characteristics of its tracking response signals, leading to the creation of a simulation model for a six-pulse converter valve that incorporates multiple series-connected thyristor stages. By examining typical statistical patterns of thyristor module degradation, the study evaluates the effects of electrical components such as snubber capacitances and equivalent thyristor resistances on the voltage profiles and temporal distribution of tracking signals across thyristor modules in the TCU. The findings reveal that degraded thyristors produce response signals earlier than their healthy counterparts, with the temporal difference increasing with the severity of degradation. Additionally, the response signal’s temporal characteristics is more reactive to insulation degradation than changes in snubber capacitance. Degraded thyristor insulation results in higher voltage loads on healthy thyristors, while thyristors with compromised snubber capacitance experience increased voltage. These insights are vital for enhancing the real-time, online assessment of valve component health through TCU tracking signals, thereby improving the reliability and operational safety of HVDC systems.