Eutrophication poses a critical challenge to global aquatic ecosystems, with the core difficulty in its remediation lying in the scarcity of sustainable technologies capable of simultaneously and efficiently removing nitrogen and phosphorus while enabling cost-effective recovery. To address this, a novel light rare-earth magnetic composite functional material was synthesized. The study systematically investigated variables including modifying agent type, matrix ratio, preparation conditions, and material dosage on nitrogen and phosphorus removal efficacy. Through optimization, a 60-mesh natural zeolite from Inner Mongolia, modified via ion exchange with 8% NaCl solution for 24 hours and calcined at 500°C, and a modified montmorillonite, prepared by mixing La2O3 with montmorillonite at a 1:1 mass ratio, stirring for 4 hours, and calcining at 500°C, were selected as the optimal precursors. Subsequently, a series of composite materials were successfully fabricated by combining the optimized modified zeolite and montmorillonite with magnetic powder, clay minerals, and a pore-forming agent in specific proportions. Material characterization and adsorption experiments demonstrated that the modification successfully preserved the basic framework structure of the matrices while achieving pore restructuring and active site anchoring. The adsorption processes for nitrogen and phosphorus were dominated by physical adsorption/ion exchange and chemical complexation, respectively, both fitting well with the two-compartment first-order kinetic model. The saturation magnetization of the resulting composites increased linearly with Fe3O4 content, indicating excellent potential for magnetic separation. Among the formulations, the JH3 composite, with a ratio of 9:4:3:2:2, exhibited the best synergistic purification performance in simultaneous adsorption tests. This study successfully developed a light rare-earth composite material possessing both synergistic nitrogen and phosphorus removal capacity and magnetic recoverability. This material offers an efficient and recoverable strategy for eutrophic water remediation, holding significant implications for advancing green and sustainable water treatment technologies.