The existing vanadium redox batteries system (VRBS) model rarely reflects the coupling effects of flow and ion diffusion, and cannot fully reflect the operating characteristics of VRBS. Therefore, based on the basic structure of vanadium redox battery (VRB) and the principle of electrochemical reaction, a VRB model of 45KW/180KWh is constructed in this paper. The model includes equivalent circuit module and electrochemical module. Through MATLAB/Simulink simulation, the model can dynamically reflect the electrochemical characteristics and external output characteristics of the battery. Then, the MWh VRBS model is constructed, which consists of VRB model with circuit series and liquid flow circuit independent. The effects of different initial SOC, internal resistance and capacity of VRBS on the dynamic characteristics of MWh VRBS were studied. The results show that the difference between VRBS leads to a higher degree of unbalance between VRBS, lower energy utilization rate of the system, lower charging and discharging capacity of the system, and finally shorten the life of MWh VRBS.