In the field of electrochemical energy storage systems, the use of in situ detection technology helps to study the mechanism of electrochemical reaction. Our group has previously in situ detected the electrochemical reaction in vanadium flow batteries by total internal reflection (TIR) imaging. In order to further improve the detection resolution, in this study, the weak measurement (WM) method was introduced to in situ detect the electrochemical reaction during the linear sweep voltammetry or the cyclic voltammetry tests with quantitative measurement of the absolute current density, which lays a foundation for replacing the TIR for two-dimensional imaging of electrochemical reactions in vanadium flow batteries, oxygen/hydrogen evolution reaction, surface treatments, electrochemical corrosion and so on.