Background and Aims <p>The symbiosis between <i>Robinia pseudoacacia</i> L<i>.</i> and rhizobia has been identified as an advanced remediation solution for Cd contamination. However, the mechanism involved in the regulatory interaction of nitric oxide (NO) and <i>Robinia</i>-rhizobia symbiosis in the remediation of Cd pollution remains unclear. We aimed to elucidate the mechanism by which NO mediates the enhancement of Cd resistance in the <i>Robinia</i>-rhizobia symbiosis.</p> Methods <p>We analyzed plant growth, Cd content and Cd chemical form, antioxidant system, nitrogen fixation capacity and endophytic community structure of <i>Robinia</i>-rhizobia symbiosis using physiological and biochemical parameters and metagenomic sequencing.</p> Results <p>NO significantly reduced Cd content in the roots of symbiosis (14.9%), increased Cd accumulation in the roots (97.2%), while significantly increasing the proportions of acetic acid-extractable Cd and Cd-oxalate in the roots. Meanwhile, NO significantly up-regulated superoxide dismutase (SOD), catalase (CAT), dehydroascorbate reductase (DHAR), and glutathione S-transferase (GST) enzyme activities and reduced malondialdehyde (MDA), H₂O₂, and O₂⁻ levels. Moreover, NO up-regulated abundance of nitrogen fixation functional genes <i>nifD</i> and <i>nifK</i> in the roots of symbiosis, with 1.75-fold and 1.08-fold, respectively. Partial least square path modeling indicated that the antioxidant system, Cd chemical form, and nitrogen fixation capacity synergistically contribute to the enhancement of Cd resistance in <i>Robinia</i>-rhizobia symbiosis.</p> Conclusion <p>This study suggests that NO improves the resistance to Cd in symbiosis by activating the antioxidant system, decreasing Cd bioavailability, and enhancing nitrogen fixation. This study provides a novel perspective on the joint restoration of heavy metal pollution by NO and microbes-woody N₂ fixing plants.</p> Graphical Abstract <p></p>