Abstract: In order to overcome shortages of groundwater pollution remediation techniques such as Pump and Treat (P&T) and Permeable Reactive Barriers (PRB), the remediation mechanism and effects of NH₄⁺-N in groundwater were studied by developing a small-scale experimental apparatus for the multi-layer enhance groundwater remediation technique (MET). The results showed that, with the influent hydraulic loading of 14.68 m³/(m²·d), ρ(NH₄⁺-N) of 25.0 mg/L and the time of continuous operation of 45 d, NH₄⁺-N removal rate at first declined, then rose steadily, and then declined, with an average of more than 90%. The ρ(NH₄⁺-N) removed by microbial nitrification and microbial assimilation was about 13.9 and 5.2 mg/L, respectively, comprising 54% and 20% of the total water ammonia. However, the ρ(NH₄⁺-N) removed by plants, permanent substrate adsorption and volatilization was about 2.9,0.7 and 0.7 mg/L, respectively, comprising 20%, 3% and 3% of the total water ammonia. Thus, the groundwater ammonia removal rate of MET reached 90%, and the goal of efficient removal of NH₄⁺-N was achieved.