The invention belongs to the field of flow batteries, and discloses an online monitoring device and method based on the
state of charge of a
flow battery. The device comprises a battery negative
electrode liquid inlet, a battery negative
electrode liquid outlet, a battery positive
electrode liquid inlet, a battery positive electrode liquid outlet, a liquid flow negative electrode half battery, a liquid flow positive electrode half battery, a liquid blocking
rubber mat, an ionic membrane, a liquid
flow battery reference detection cavity, a valve, a main pipeline and a
liquid storage device. The method comprises the following steps of firstly, adding
electrolyte which is homopolar with a liquid flow half battery into a reference detection cavity of the liquid
flow battery, when the battery starts to run, monitoring open-circuit voltages between an electrode A and an electrode B and between the electrode B and an electrode C in real time, and respectively monitoring the
state of charge of the
electrolyte of the positive and negative electrodes to eliminate an open-circuit
voltage difference value caused by
permeation, and eliminating an open-circuit
voltage difference value caused by valence state attenuation, so that real
state of charge monitoring is realized. Therefore, the
electrolyte utilization rate is improved, and the flow battery performance is improved; meanwhile, charging and discharging can be carried out more safely, and the service life of the battery is prolonged.