The invention relates to an all-vanadium redox flow energy storage battery system and a subsystem power consistency adjustment method thereof. The adjustment method is characterized in that: a blending pipeline is arranged in the all-vanadium redox flow energy storage battery system to blend the positive and negative electrolyte of each subsystem and then redistribute to each electrolyte storage tank, internal resistance consistency of each subsystem and positive and negative electrolyte charging state SOC consistency of each subsystem are adjusted in the process of battery working, thus the power consistency of subsystems in the working process is guaranteed. According to the invention, the invention is especially suitable for the application of the all-vanadium redox flow energy storage battery system in large-scale energy storage field, long-term stable operation of the all-vanadium redox flow energy storage battery system is guaranteed, and the electrolyte capacity attenuation of the all-vanadium redox flow energy storage battery system caused by series-parallel connection is effectively postponed.