Digital holographic interferometry was used to measure concentration change distribution of the solution at the interface of electrode/solution during electrochemical reactions. In experiment, the first 1.6 s of the activation processes of potentiostatic current oscillation on iron in 0.5 mol/dm3 H2SO4 solution was studied. With the introduction of carrier fringes in digital holographic interferometry, Fourier analysis method was used to analyze interference patterns and calculate their dynamic changes conveniently. The phase difference of object wave front, which was caused by the change of the solution′s concentration during the electrochemical reaction, was calculated from interference patterns to reflect the concentration change distribution. The obtained results have shown that the maximum phase difference caused by the concentration change of the solution was 41.2 rad and the corresponding change of solution′s refractive index was 0.0021 while the electrochemical reaction was at 1.6 s. The reconstructed images, which were distribution of the phase difference of object wave front, reflected the changes such as concentration distribution, diffusion layer, etc.. It provided a new method to detect and analyze dynamic concentration changes.