Abstract: The twist of the split-spun yarn was studied by the principle of the solo-spinning and mechanical theories that have three sections (conjunction points, the fasciculus above this point, and the yarns below conjunction points). We analyzed the twist of the split-spun yarns, the twist producing and distribution along the split-spun yarns. Finally, we concluded that there are correlation between the twist of fasciculus, the twist of yarns, and the condition of the fasciculus. We also concluded that the twist of the fasciculus is not a fixed value and so on. And, from the analysis of the twist for the conjunction points in the split-spun yarn, we brought forward the rules concerning the ratio of fasciculus to yarn twist. And, The correlation between the twist of fasciculus and the fibers’capability was investigated, pointing out that only when the twist of split-spun yarn are in critical value, the index of yarn will be the best.