Abstract: The contamination of soils and groundwater caused by landfill leachate is increasingly prominent. Given the distinctive electrical properties of leachate, such as low resistivity, high polarization, high time constant, and low-frequency correlation coefficient, this study performed three-dimensional finite element numerical simulations of landfills using the spectral induced polarization (SIP) method. The aim is to explore the theoretical effects of this method in detecting landfill leachate. First, this study conducted forward modeling for typical geoelectric models using the algorithm developed in this study. The result revealed a maximum relative error between the numerical and analytical solutions of less than 2.5%, demonstrating the algorithm's accuracy and effectiveness. Second, the parameters of the SIP model were set based on the actual electrical characteristics of landfills, ensuring that the numerical simulations closely reflected actual conditions. Finally, SIP anomaly responses were compared and analyzed for landfill leachate leakage under different scenarios. The results indicate that the leachate locations can be accurately delineated using the apparent complex resistivity's phase and apparent dispersion, regardless of whether landfills are equipped with high-resistivity impermeable walls. For leachate plumes of the same scale, shallower locations corresponded to more pronounced anomaly morphologies of apparent complex resistivity's phase and apparent dispersion. Compared to the direct current resistivity method, the SIP method can detect richer underground electrical parameters, achieving better application effects in detecting landfill leachate.