Vanadium battery has fast and large capacity charge and discharge characteristics,and the concentration and stability of the battery electrolyte are the key to the electrolyte performance.In actual,with higher acidity and higher concentration of the vanadium battery electrolyte,the ion-pair is dominant.The ion-pair dissociation constant is one of the important thermodynamic data related to battery performance.The vanadyl sulfate conductivity in aqueous solution was determined using the conductance method at 298.15 K.Using the origin data fitting,the limiting molar conductance is obtained,and then by the improved Ostwald dilution law and the Davies equation,the activity coefficient is solved so as to obtain the ionic strength of the true solution.Using the Fuoss method,the dissociation constant of vanadyl sulfate ion-pair was calculated.At last,the vanadyl sulfate limiting molar conductance(A_0) is 174.8251748 S·dm~2·mol~(-1),and the vanadyl sulfate ion-pair dissociation constant K_d is0.002636367,and then other thermodynamic properties can be studied. Vanadium battery has fast and large capacity charge and discharge characteristics, and the concentration and stability of the battery electrolyte are the key to the electrolyte performance.In actual, with higher acidity and higher concentration of the vanadium battery electrolyte, the ion-pair is dominant The ion-pair dissociation constant is one of the important thermodynamic data related to battery performance. The vanadyl sulfate conductivity in aqueous solution was determined using the conductance method at 298.15 K. Using the origin data fitting, the trimerization of molar conductance is obtained, and then by the improved Ostwald dilution law and the Davies equation, the activity coefficient is solved so as to obtain the ionic strength of the true solution. Using the Fuoss method, the dissociation constant of vanadyl sulfate ion-pair was was calculated. At last, the vanadyl sulfate trioxide molar ratio (A_0) is 174.8251748 S · dm ~ 2 · mol -1, and the vanadyl sulfate ion-pair dissociation constant K_d is0.002636367, and then other thermodynamic properties can be studied.