High-intensity focused ultrasound (HIFU) transducers are a core component of focused ultrasound ablation surgery (FUAS) systems, whose electric impedance spectrum is an important index to determine working parameters that significantly affect FUAS systems performance.Real-time online monitoring of this spectrum is significantly beneficial.In this study, based on pulse response time-domain measurement, by merging the detected pulse signal serial into the FUAS operational electric driving signal sequence of the HIFU transducer, a real-time online monitoring system for the electric impedance spectrum of the HIFU transducer was constructed on the LabVIEW platform.Highly reproducible accurate measurements towards the magnitude and phase spectrum of the HIFU transducer electric impedance were achieved.Subsequently, a monitoring system was applied to determine dynamic changes in the electric impedance of the HIFU transducer under extreme working conditions.These include long-time service, high electrical driving power and duty cycle.The results demonstrate that the proposed system accurately monitors the HIFU transducer eigen frequencies drift, alongside nonlinear changes in impedance magnitude and phase.This paper presents a technical solution for real-time online monitoring of HIFU transducer impedance during FUAS, and provides feedback for drive parameter adjustment, which has practical application value for HIFU transducer design optimization and energy loss mechanisms.