Abstract: Landfill leachate, a highly contaminated wastewater, poses significant threats to surrounding ecosystems if not properly treated. The biochemical-dual membrane process, typically comprising a two-stage anoxic/oxic (A/O) membrane bioreactor (MBR) followed by nanofiltration (NF) and reverse osmosis (RO), has become a mainstream technology for leachate treatment in China due to its high efficiency and stable effluent quality. However, challenges such as high energy consumption and secondary concentrate pollution call for a comprehensive diagnostic approach beyond conventional indicator evaluations. To systematically assess operational efficiency and identify energy-saving potential, this study established a dual-perspective framework integrating material flow and energy consumption analyses. Focusing on a full-scale "two-stage A/O-MBR-NF-RO" process in a Southern China environmental park, detailed carbon (C), nitrogen (N), and phosphorus (P) mass balance models were developed alongside an energy consumption structure model based on long-term monitoring and full-process sampling. The results indicated that the effective removal rates of COD, total nitrogen (TN), and total phosphorus (TP) in the biological treatment units were 83.31%, 84.11%, and 93.10%, respectively. The subsequent NF-RO units intercepted over 95% of the residual pollutants, ensuring that the final effluent consistently met discharge standards. Material balance analysis revealed that the balance rates for C and P exceeded 96%, indicating high data reliability; however, nitrogen exhibited a material loss of approximately 10%. This loss was primarily attributed to incomplete nitrification-denitrification caused by dissolved oxygen (DO) interference in the anoxic zones under a high reflux ratio. The specific electrical energy consumption for treating the leachate was determined to be 40.44 kW·h/m³. Energy structure analysis showed that energy consumption in the biological treatment unit accounted for 53.37% of the total, mainly utilized for biochemical reactions. In contrast, energy consumption in the advanced treatment unit constituted 93.75% of its respective subsystem′s input, primarily consumed for phase transfer of pollutants. Both units faced challenges of high energy consumption and low energy utilization efficiency. Based on these analyses, improvement strategies were proposed with quantitative metrics. These included optimizing the nitrification recycle ratio from 1500% to a range of 800%–1000% and controlling the DO concentration in the anoxic zone to below 0.2 mg/L. Furthermore, the partial introduction of an energy-efficient anammox-based process was recommended. Quantitative predictions indicated that implementing these measures could enhance the TN removal efficiency to 88%–90%, reduced the energy consumption of recycle pumps by approximately 30%, decrease aeration energy demand by about 60%, and eliminate the need for external carbon sources, leading to a 20%–30% reduction in the overall energy consumption of the biochemical unit. This study provides a scientific basis for refined operational control and energy-saving retrofits in leachate treatment processes.