Abstract: To address the critical bottlenecks of cathodic alkaline precipitation and anodic complex back-migration in electrokinetic remediation of low-permeability heavy metal-contaminated loess, this study developed a novel composite permeable reactive barrier (PRB) material by combining agricultural compost with biochar, and placed it in the anode zone. The effects of compost-to-biochar mass ratios (0:1, 1:1, 7:3, 9:1, and 1:0) on the electrokinetic removal efficiency of Cu- and Pb-contaminated loess were systematically investigated, with the interfacial reaction mechanisms elucidated by Raman and FTIR spectroscopy. The abundant hydroxyl (—OH) and carboxyl (—COOH) groups on the composite surface captured Cu-EDTA and Pb-EDTA complexes migrating toward the anode through coordination exchange and surface precipitation, converting them into insoluble phases such as CuCO₃, PbCO₃, Cu(OH)₂, and Pb(OH)₂, thereby achieving in-situ immobilization of heavy metals. At a compost-to-biochar ratio of 1:1, the composite exhibited optimal electrical conductivity and adsorption capacity, increasing the system current by approximately 18% compared to the control without PRB. In the middle-to-rear soil sections (S4-S6), Cu removal efficiency reached 42.3%-62.5%, representing a 15-25 percentage-point improvement over the control, while Pb removal efficiency reached 30.2%-55.7%, with a 10-20 percentage-point increase. After remediation, the bioavailable fractions of Cu and Pb in the soil were reduced by 58.6% and 47.3%, respectively. By fully utilizing agricultural waste resources and operating through a synergistic mechanism of functional group-mediated chemisorption and surface precipitation, this compost-biochar composite PRB material offers a cost-effective and sustainable in-situ remediation solution for low-permeability heavy metal-contaminated sites.