The invention discloses a capacitance online monitoring device for a parallel capacitor. The capacitance online monitoring device for the parallel capacitor comprises a current sensor module, a wireless terminal module, a ZigBee receiving and transmitting module and an upper computer, wherein the current sensor module is connected with the wireless terminal module, the ZigBee reserving and transmitting module and the upper computer in sequence. The current sensor module transmits signals to the wireless terminal module, and the wireless terminal module transmits data to the upper computer through the ZigBee receiving and transmitting module. The wireless terminal module comprises a main control unit, an A/D converting unit and a wireless receiving and transmitting unit, and the main control unit is connected with the A/D converting unit and the wireless receiving and transmitting module respectively. The capacitance online monitoring device for the parallel capacitor is high in reliability and capable of carrying out monitoring in real time, reduces the workload of checking and maintenance greatly, improves the stability of a power grid power supply system, and plays a very important role for the normal power supply of the whole electric power system.