Abstract: In order to improve the electrochemical activity and energy density of negative electrolyte of vanadium redox flow battery,the viscosity,conductivity and electrochemical performances of the negative electrolytes at different compositions were investigated.The results show that the vanadium concentration and sulfuric acid concentration affect the viscosity,conductivity and electrochemical activity of the negative electrolyte by changing the hydrogen ions concentration and aggregation state of vanadium ions.The viscosity of the negative electrolyte increases with increase of the vanadium concentration and sulfuric acid concentration,and the conductivity increases with increase of the sulfuric acid concentration but decreases with increase of vanadium concentration.Appropriate sulfuric acid concentration can improve the electrochemical activity of the electrolyte,while increasing the vanadium concentration restrains the mass transfer and charge transfer processes for the negative electrolyte.When the vanadium concentration is 2.0 mol/L and sulfuric acid concentration is 2.0 mol/L,the electrolyte shows the best electrochemical activity and reversibility,with the mass transfer rate of(1.39~2.25)×10^-7 cm²/s and the charge transfer rate of 1.74×10^-5 cm/s.