This standard specifies the terms and definitions, product classification and identification, basic requirements, technical requirements, test methods, inspection rules, marking, packaging, transportation, storage and quality commitment of flat polyester pre-oriented yarn. This standard is applicable to pre-oriented polyester yarns with a total line density of 75 dtex to 600 dtex, a single filament line density of 0.5 dtex to 6.0 dtex, flat cross-section, natural color, glossy and semi-matt flat polyester.