Abstract: Siro cotton/Spandex core-spun yarn which possesses the advantages of good evenness and little hairiness of siro yarn and brings into play the power stretch of Spandex fiber is ideal for production of all kinds of elastic fabric.The relationship between main technical parameters(twist factor,roving interval,pre-drafting) and yarn quality index(hairiness,strength,breaking elongation,evenness) of siro cotton/Spandex core-spun yarn was tested and optimized,providing a reference for spinning siro cotton/Spandex core-spun yarns.