In this paper, by comparing the properties of polyester/cotton/silk three-component Sirofil composite yarn and traditional cotton yarn, polyester/cotton core-spun yarn, silk/cotton two-component Sirofil composite yarn, the structural characteristics of three-component Sirofil composite yarn and the relationship between its structure and property were explored. There was the inhibition effect of cotton fiber on polyester filament, so the frictional and cohesive force between cotton fiber and polyester filament could be enhanced. The tenacity of polyester filament and cotton fiber were very good and the wrapping effect of raw silk could enhance the cohesive force between cotton fibers, cotton fiber and polyester filament. Therefore, the strength of composite yarn was obviously increased and the abrasive resistance and anti-stripping wool property were also greatly enhanced. Secondly, hairiness between raw silk and fiber strand was very easily captured by raw silk and there was the wrapping effect of raw silk on fiber strand in the composite spinning, so some hairiness was covered by raw silk, which could decrease the length of hairiness or eliminate hairiness. Furthermore, much more uniform raw silk and polyester filaments were added, which could increase the yarn evenness of Sirofil composite yarn.