Abstract: With the continuous development and renewal of underground pipeline networks in China, the corrosion durability of buried metallic materials under complex geological and climatic conditions has become a critical research topic for ensuring the safe operation of urban lifeline infrastructure systems. Limited by static sampling approaches and fragmented data characterization, traditional soil corrosivity evaluation methods still exhibit certain limitations in supporting long-term corrosion risk identification and refined operation and maintenance of underground pipeline networks. To achieve a quantitative evaluation of the long-term corrosion of metals in soil environments, this study employs electrochemical impedance spectroscopy (EIS) to investigate the corrosion characteristics of metals in soils under coupled salt–thermal conditions. Experimental and modeling results indicate that, the corrosion behavior of metals in soil is jointly governed by the mass transfer characteristics of the soil medium, the structure of the interfacial soil particle adhesion layer, and the electrochemical reaction processes of the metal. The dissolution reaction current density IF, calculated based on the charge transfer resistance Rt, decreases with decreasing temperature and increases with increasing salinity; however, within the freezing temperature range, the influence of salinity is markedly weakened. Comparison with the results obtained using the polarization curve method specified in current standards shows that IF is consistently lower than the corrosion current density icorr, the EIS method effectively distinguishes interfacial capacitive effects from Faradaic reaction processes, yielding corrosion evaluation results that more closely represent the natural corrosion state of metals in soil. The results of this study provide a theoretical basis and technical reference for nondestructive testing and engineering–oriented evaluation of soil–induced metal corrosion.