Abstract: A mathematical model of twisting torsion of the slub yarn has been developed through the pole torsion model based on the distribution of the torsional stress on the ring-spun slub yarn during twisting.The influence of four parameters(basic yarn diameter,slub diameter,slub space and slub length)on the distribution of twist was analyzed using this model.The results showed that the twist of the slub is always less than the designed,which is chiefly influenced by the ratio of the slub diameter to the basic yarn diameter,and increase of the ratio will decrease the twist;while the twist of basic yarn is always more than the designed,which is mainly influenced by the ratio of the slub length to the slub space,the increase of the ratio will increase the twist.The effect of the distribution of twist on the yarn strength was also analyzed,and verification experiment was performed.In general,the strength of the yarn is influenced more by the increased fiber quantity in the yarn than by the decrease of the slub twist.Therefore,the strength of the slub is higher than that of the basic yarn. The strength of the whole slub yarn is very close to that of the common yarn with the same twist as the basic yarn.