Abstract: Due to its abundant resources, low cost, and tunable structure, hard carbon is considered a highly promising anode material for sodium-ion batteries. However, its sodium storage capacity largely depends on precise control of its microstructure. In this study, a series of humic acid-based hard carbon anode materials were successfully synthesized using KOH activation combined with high-temperature carbonization. The regulation mechanisms of activation temperature (400, 500, 600, 700, 800°C) on their microstructure and sodium storage capacity were systematically investigated. The results indicate that as the activation temperature increases, the pore structure of the material gradually develops, the specific surface area and total pore volume continuously increase, and the carbon interlayer spacing and carbon phase structure undergo significant evolution. Among these, the 600°C-activated sample (HC-600) exhibited the highest proportion of disordered carbon structure (43%), a well-developed hierarchical pore structure (specific surface area of 339.26 m2/g, mesopore content of 45.97%), and moderate interlayer spacing, forming a structural system conducive to ion storage and transport. Electrochemical testing revealed HC-600 exhibits optimal sodium storage performance, achieving an initial reversible specific capacity of 245 mAh/g at 20 mA/g current density with a first-cycle coulombic efficiency of 69.6%. After 1000 cycles at 500 mA/g, the capacity retention rate remained at 82.9%, while demonstrating excellent rate capability. Kinetics analysis revealed that the sodium storage process in HC-600 is synergistically regulated by surface pseudocapacitive behavior and diffusion-controlled behavior, exhibiting a multi-mechanism synergistic sodium storage characteristic of “adsorption-intercalation-filling.”