The phosphate material Na3V2(PO4)3 is one of promising cathodes for Na-ion batteries owing to its superior electrochemical reversibility. However, the high-potential V4+/V5+ redox couple (4.0 V vs. Na+/Na) in pure Na3V2(PO4)3 cathode is not activated, resulting in a limited energy density. Although conventional single-metallic substitutions can activate V4+/V5+ redox plateau, the energy density has no significant improvement due to the limited capacity of V4+/V5+ redox plateau. Here, we propose a bi-metallic (Al3+ and Fe3+) substitution strategy, which can increase the reversible capacity of V4+/V5+ couple via lowering the energy needed during desodiation process, thus realizing a remarkable improvement of energy density. Moreover, we reveal that Fe3+substitution can improve the rate performance of cathode by reducing band gap and Na-ion diffusion activation energy. As a result, the designed Na3V1.5Al0.3Fe0.2(PO4)3 cathode delivers a high energy density of 399.7 Wh kg-1 (capacity 116.2 mAh g−1, average voltage 3.44 V) and a high rate capability (91.2% capacity retention from 0.1 C to 20 C), as well as superior cycling stability (89.5% capacity retention after 8000 cycles at 10 C). In addition, we demonstrate a 0.8 Ah 18,650-type Na3V1.5Al0.3Fe0.2(PO4)3//hard carbon full cell with 92.4% capacity retention over 400 cycles at 0.5 C. This work presents the design of high-performance phosphate cathode via bi-metallic substitution, boosting the development of practical Na-ion batteries.