Abstract: The core_spun yarn,covering polyester filament with cotton, has such problems as much hairiness,relax structure, lowered wear resistance and pilling tendency. To solve these problems and facilitate the production of the fancy yarn or blended color yarn, designed a feeding and tension control device with the front roller with grooves and successfully spun a tri-component composite yarn with special structure by one-step on the traditional ring spinner. On the basis of analysis of the spinning process and mechanism, the technology parameters influencing the properties of the yarn are put forward.