Abstract: A preparation method of anionic polyester fiber was researched.Polyester chips were crystallized,dried up,and grinded into powder,and then mixed with dispersant and anionic powder whose surface has been modified.The mixed powder was extruded and chipped,thus obtained the anionic polyester chips which were used as sheath,and ordinary PET as core,sheath-core bi-composite fibers were made.It indicated by testing that the chips containing 4 percent anionic powder have excellent spinnability.This sheath-core bi-composite fiber has good serviceability and capacity of releasing anion.