Sodium-ion storage devices are highly desirable for large-scale energy storage applications owing to the wide availability of sodium resources and low cost.Transition metal nitrides(TMNs)are promising anode materials for sodium-ion storage,while their detailed reaction mechanism remains unexplored.Herein,we synthesize the mesoporous Mo3N2 nanowires(Meso-Mo3N2-NWs).The sodium-ion storage mecha-nism of Mo3N2 is systematically investigated through in-situ XRD,ex-situ experimental characterizations and detailed kinetics analysis.Briefly,the Mo3N2 undergoes a surface pseudocapacitive redox charge stor-age process.Benefiting from the rapid surface redox reaction,the Meso-Mo3N2-NWs anode delivers high specific capacity(282 mAh g-1 at 0.1 A g-1),excellent rate capability(87 mAh g-1 at 16 A g-1)and long cycling stability(a capacity retention of 78.6%after 800 cycles at 1 A g-1).The present work highlights that the surface pseudocapacitive sodium-ion storage mechanism enables to overcome the sluggish sodium-ion diffusion process,which opens a new direction to design and synthesize high-rate sodium-ion storage materials.