In the present study, the Erigeron canadensis L., a typical invasive plant in Southwest China, was utilized as the raw material to prepare original biochar (ECL), a rare earth element La–modified biochar (La–ECL), and a rare earth element La coupling cationic surfactant [cetyltrimethylammonium chloride (CTAC)]–modified biochar (La/CTAC–ECL). These materials were then added to simulated permeable reactive barriers (PRBs) and their nitrate (NO₃⁻) contaminant remediation performances were evaluated in groundwater. The results show that the breakthrough time for NO₃⁻ in a simulated PRB column increases as the concentration of the influent NO₃⁻ and the flow rate decreases, whereas with the increases of filler particle size and the height of the filler in the column initially increases, and then decreases. Considering an initial NO₃⁻ concentration of 50 mg L⁻¹, and a filler particle size range of 0.8–1.2 mm, the maximum adsorption capacity of the La/CTAC–ECL column for NO₃⁻ is 18.99 mg g⁻¹ for a filler column height of 10 cm and an influent flow rate of 15 ml min⁻¹. The maximum quantity of adsorbed NO₃⁻ of 372.80 mg is obtained using a filler column height of 15 cm and an influent flow rate of 10 ml min⁻¹. The Thomas and Yoon–Nelson models accurately predict the breakthrough of NO₃⁻ in groundwater in the simulated PRB column under different conditions, and the results are consistent with those from dynamic NO₃⁻ adsorption experiments. TEM, XRD, FTIR, and XPS analyses demonstrate that the modification using the La and CTAC improves the surface structure, porosity, permeability, and configuration of functional groups of the biochar. The mechanisms of NO₃⁻ removal from groundwater using the La/CTAC–ECL include pore filling, surface adsorption, ion exchange, and electrostatic adsorption. The composite La/CTAC–ECL exhibits a superior potential for the remediation of NO₃⁻ contaminated groundwater.