Transition metal sulfides are hindered in their application in high-rate sodium-ion batteries due to poor conductivity, slow kinetics, and low electrochemical cycling life. This paper proposes a novel modification method by substituting sulfur in transition metal sulfides with selenium, resulting in a series of micron-sized Cu3.21Bi4.79S9-xSex materials. Structural characterization analysis, electrochemical performance tests, and theoretical calculations demonstrate that Se substitution has a dual effect on sodium ion storage. Increasing Se substitution enhances the material’s electronic conductivity and enlarges the interlayer spacing, thereby improving the Na ion diffusion coefficient. However, excessive Se substitution reduces the active sites, decreasing the sodium storage capacity. When the Se substitution ratio is?x??=?1.8, Cu3.21Bi4.79S7.2Se1.8 exhibits excellent reversible specific capacity (388.9 mAh/g after 300 cycles at 2 A/g) and outstanding rate performance (capacity retention of 91.7?% from 1 A/g to 10 A/g), as well as ultra-long cycling life (301.7 mAh/g after 5000 cycles at 15 A/g). This anion substitution method of replacing sulfur in metal sulfides provides a strategy for enhancing the rate performance of sodium-ion battery metal sulfide anodes through electronic structure engineering modification.