This standard specifies the terms and definitions, classification and identification, technical requirements, test methods, inspection rules and marks, Encasement, transportation and storage requirements for cation dyestuff dyeable modified polyester staple fibers. Applicable to circular cross-sections with a linear density of 1.2 dtex~ 3.0 dtex, and the third monomer content is greater than or equal to 2.0% of cation dyestuff dyeable modified polyester staple fibers. Normative reference documents include chemical reagent test methods, Spinning & weaving material performance and test terms, Spinning & weaving product chemical fibers, chemical fiber moisture regain test methods, numerical revision rules, etc. Definitions for production batches, inspection batches and cation dyestuff modified polyester staple fibers are given in the terminology and definitions section.