In recent years, the damage of substation equipment caused by reactive power switching and the fire of dry-type air-core reactors have occurred frequently, which seriously affects the safe operation of the power grid.The opening overvoltage generated during the opening process of the circuit breaker is one of the main reasons for equipment failure. The frequency and amplitude of the transient overvoltage caused by re-ignition are much higher than the normal switching transient voltage. Therefore, it is necessary to Attention and assessment of re-ignition and its impact on equipment insulation. Whether the circuit breaker (especially for the vacuum short-circuit circuit breaker) switching reactive equipment produces re-ignition is related to two factors: the reactive switching characteristics of the circuit breaker itself,and the parameters of the reactive circuit (including cable length and equipment equivalent capacitance, etc.), the unreasonable selection and the mismatch between the two lead to the main reason for the high frequency of re-ignition. In the design stage of the substation, the selection of parameters of reactive power circuit equipment, conductors, and whether to install a voltage limiting device has not been specified from the perspective of suppressing reactive switching transient voltage. The characteristics of the switching reactive power equipment of the vacuum circuit breaker itself do not require factory and new installation tests. The dispersion of different equipment parameters leads to differences in transient overvoltage levels, which need to be evaluated; The magnitude of the overvoltage and its hazard are also lack of monitoring and control, resulting in frequent transient faults of reactive power equipment during operation, and the cause of the fault is difficult to trace. In response to this problem, this paper discusses the re-ignition rate of reactive power circuit switching and the peak oscillation voltage as evaluation indicators to measure the operating state of reactive power equipment. And the necessity to carry out the monitoring of transient characteristics of reactive power equipment switching in the actual operating state,Aiming at the problem of lack of online monitoring methods for reactive power switching, an online monitoring method for reactive power switching transient process based on high-frequency response of bus PT is proposed, which fills the gap of reactive power equipment operating status monitoring.