Shunt reactors and capacitor banks are frequently operated to maintain the system voltage, therefore it requires a reliable Circuit Breaker (CB) conditions. However, there is a case of CB fault during the process of extra-high voltage (EHV) reactors switch off. This paper investigated the cause of the fault through the simulation and field data analysis. The result shows that the fault which occurs in the EHV reactor CB is caused by the emergence of high transient recovery voltage (TRV) value and rate of rise of recovery voltage (RRRV). A high TRV and RRRV value caused arcing, which can melt CB A2 contacts. When contacts melting have been occurred, the two CB contacts can coalesce which create an uneven shape with a smaller cross-sectional area of the contacts. Current flow through this contacts produce heating in the CB A2 chamber, and then the gas expanded rapidly causing an explosion in the CB A2. To prevent the similar fault of the EHV reactor CB, it is necessary to increase the capability of CB in handling TRV and RRRV, as well as asses the condition of the grading capacitor in the CB routinely.