Purpose <p>Phytoremediation using <i>Pongamia</i> <i>pinnata</i> has proven effective for restoring the ecological environment in the vanadium (V) – titanium (Ti) magnetite mining area. However, the interactive effects between soil nutrient element cycles during the restoration process remain poorly understood. </p> Methods <p>This study systematically investigated changes in soil nitrogen (N) speciation, enzyme activities, N functional genes, and bacterial community composition during ecological restoration with <i>P.</i> <i>pinnata</i> at the V-Ti magnetite tailings area. A particular focus was placed on elucidating the interrelationships between soil carbon (C) and N dynamics. </p> Results <p><i>P.</i> <i>pinnata</i> remediation significantly enhanced soil N-cycling. Specifically, the three-year extension of remediation period increased four soil hydrolyzable organic N fraction by 34.70%-90.92%, and NH₄⁺–N and NO₃⁻–N rose by 25.70% and 16.11%, respectively. The activities of protease, urease, and nitrate reductase respectively increased by 6.77%, 188.24%, and 187.01%. Functional genes associated with the N-degradation pathway comprised 61.60% to 74.06% of total N-cycling genes. Furthermore, <i>P.</i> <i>pinnata</i> remediation enriched four key bacterial phyla of <i>Actinobacteria</i>, <i>Proteobacteria</i>, <i>Bacteroidetes</i> and <i>Chloroflexi</i> to drive soil C and N transformation, while also tightening the correlation among C- and N-cycling genes. Notably, C-cycling genes positively affected N components, whereas N-cycling genes negatively modulated the activity of C-transformation enzyme following restoration. </p> Conclusions <p>These findings revealed that <i>P.</i> <i>pinnata</i> remediation strengthened interaction between soil C- and N-cycling, thereby improving the ecological function of barren soil in the V-Ti magnetite mining area.</p>