Abstract: Nitrate pollution has received high attention due to its characteristics such as universality and the high carcinogenicity rate of its reduction products. The permeable reactive barrier (PRB), as an efficient and low-energy-consuming remediation technology, has great application prospects in the remediation of nitrate pollution. Among the commonly used wall remediation materials, zero-valent iron (ZVI) and activated carbon (AC) materials have great potential for the remediation of nitrate. However, currently, there is a lack of research on the long-term operational stability of the PRB technology, and the monitoring methods are limited. The induced polarization method, due to its greater sensitivity to the changes in the microscopic scale properties of porous media, is more helpful in characterizing the characteristics of the PRB filling medium. Therefore, it is urgent to explore the PRB operation performance monitoring technology based on the induced polarization method. This study focuses on the reaction mechanism of ZVI-AC for remediating nitrate pollution, as well as the feasibility of using the SIP technology to monitor the remediation process of nitrate pollutants by ZVI-AC materials. The spectral induced polarization method (SIP) in the frequency domain is used to monitor the process of remediating nitrate pollution by the composite material of zero-valent iron and activated carbon, and the remediation effect is comprehensively analyzed in combination with means such as hydrochemistry, scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS). The results show that: (1) ZVI-AC can give full play to the synergistic effect of the composite material. By adsorbing the oxidation products of ZVI with AC, the adhesion of these products on the surface of iron particles is reduced, thereby extending the service life of ZVI. (2) The polarizability can continuously decrease within the range of 0.6 to 0.7 along with the decrease in the nitrate removal rate, while the normalized relaxation time is positively correlated with the remaining nitrate removal rate and the volume of iron particles, showing a strong indicative effect. The experimental results provide an important theoretical basis for the induced polarization method to serve as a technical means for providing low-impact and long-term monitoring for PRB in engineering practice.