【Objective】Climate change and the continuous impact of high-intensity human activities are intensifying soil acidification and has caused serious harm to the ecological environment and agricultural production. In recent years, studies on acid soils have focused on the effects and related mechanisms of soil conditioners on physicochemical properties and crop production, but the combined application of electrochemistry theory and other interdisciplinary principles have been given less attention. Electrochemical impedance spectroscopy(EIS)is an electrochemical measurement method using small-amplitude sinusoidal potential(or current)as a disturbance signal. Its application in the soil field has attracted much attention. In this study, EIS was combined with soil physical and chemical properties to analyze the electrochemical mechanism of biochar in improving acid soils. 【Method】A field study was conducted to amend acid soil by applying biochars produced from five biomass materials (rice straw, maize straw, wheat straw, rice husk, and bamboo). The EIS was used to study the influence of different biochars on the electrochemical characteristics of acid soil. 【Result】Results showed that the equivalent circuit topology structure was the same in different biochar-amended treatments, but the circuit component parameters were different. The equivalent circuit model was the charge transfer resistor R₃ and diffusion resistor R_w at the electrode-solution interface in series, and in parallel with CPE. This part was connected in series with the soil porous layer resistor R₂, and then in parallel with the soil porous layer capacitor C₁. Finally, it was connected in series with pore solution resistor R₁. The addition of biochar had regular effects on Nyquist and Bode diagrams. The Nyquist diagram was in the form of arcs in the high-frequency region and oblique lines in the low-frequency region. The intercepts of each curve and x-coordinate corresponded to the resistance R₂ of the soil porous layer in an equivalent circuit, and a radius of each to a charge transfer resistance R₃. In the Bode diagram, the impedance modulus of the modified soil amended with different biochars tended to decrease as the frequency increased. By fitting the equivalent circuit with Z-view software, it was found that the influence of different biochars on the parameter values of each element was related to changes in soil physicochemical properties. The addition of biochar increased soil contents of total soluble salts and CEC, and the concentration of free-moving ions increased, thus the electrochemical characteristics showed that the pore solution resistance R₁ decreased. Since biochar was almost non-conductive, the conductive capacity of improved soil decreased, and the electrochemical characteristics showed that resistance R₂ of the soil porous layer increased while capacitor C₁ decreased. The cations of acid soil neutralized by biochar slowed down the process of charge transfer, increased the reaction resistance, and weaken the ability to store charge. Thus, this reduced the reaction speed and made the system more stable. The electrochemical characteristics were shown as the increase of transfer resistance R₃ and diffusion impedance coefficient W, as well as the decrease of CPE_-T value. 【Conclusion】The decrease of R₁ indicated the increase of soil water-soluble salt content and CEC. The increase of R₂ and the decrease of C ₁ indicated that the conductivity of the soil medium system decreased. The changes of R₃, W and CPE_-T indicated the charge transfer ability and overall stability of the soil system. The fitting parameters revealed the influence of modified acidification on soil pH and soluble base ions content to a certain extent, which enriched the scope of electrochemical impedance spectroscopy (EIS).