The invention relates to a reactive power compensation protective device in a power transmission and transformation system, and belongs to the technical field of reactive power compensation in the power transmission and transformation system. The technical scheme is that a plurality of single capacitors (11) are connected in parallel to form string sections of high-voltage parallel capacitor groups; each string section is connected with a discharging coil (12) in parallel; a current unit (16) which contains a current sensor is arranged on each capacitor branch of each single capacitor; a background host processes received current signals of all the current units and received voltage signals of all the discharging coils, and transmits data to a protective module. According to the reactive power compensation protective device in the power transmission and transformation system, the sensitive protection on discharging coil failures and each capacitor can be realized; the most sensitive protection and failure warning on the high-voltage parallel capacitor groups can also be realized earliest; the reuse rate of reaction equipment is improved; the operation reliability of a reactive compensation device is improved; major failures are avoided as far as possible; the protection sensitivity is improved; failure equipment is cut in time; serious failures are avoided.