Rechargeable batteries electrodes are mainly classical oxides with single structure, but their performance is insufficient to meet the growing energy storage needs of modern-society. Recently, composite-structure materials with great improvements in electrochemical performance have been developed. However, little research has been conducted on these materials with regard to adjusting their structures and further controlling their electrochemical performance. Herein, composite-structure Na2/3Ni1/3−xFexTi2/3O2 (0 ≤ x ≤ 1/3) electrodes for sodium-ion batteries were designed on the basis of results from in-situ high-temperature X-ray diffraction. Triphase compositions of P2-Na2/3Ni1/3Ti2/3O2, tunnel-Na2.65Ti3.35Fe0.65O9, and tunnel-NaFeTiO4 were prepared, and Na+ insertion/extraction in different structures was observed using in-situ electrochemical X-ray diffraction. An optimum electrode with 46% P2-structure presented the best comprehensive performance: 105mAhg−1 initial reversible capacity along with 86.5% capacity-retention after 1500 cycles. This work opens a new field for designing and adjusting composite electrodes for better electrochemical performance, not limited for sodium-ion batteries but also for other advanced battery-systems.