In this study, the electrochemical reactions along with the corresponding temperature change in the vanadium acid solutions have been investigated by the thermo-electro-chemistry method for the first time. It turned out that the electrochemical oxidation of V(II) and reduction of V(V) are both exothermic, so substantial heat could be created by the electrochemical reaction during the discharging process, which may adversely affect the stability and efficiency of the VRFB. The temperature change characters of different electrochemical redox reactions imply that lower temperature may be advantageous for the discharge process, while higher temperature is helpful to the charge process. Besides, oxygen evolution as a main side reaction along with the oxidation of V(IV) is seen to occur at a relatively lower potential and highly depends on the vanadium ion concentration in the electrolyte. Moreover, it is found that the V(III)/V(IV) solution is more likely to suffer from oxygen evolution in oxidation processes and hydrogen evolution in reduction processes than pure V(IV) and V(III) solutions. These results demonstrate that the thermo-electro-chemistry method shows great significance and application prospect in investigating the electrode kinetics and will be helpful to optimize the work conditions and related components in a VRFB.