The effect of spinning speed on yarn quality at self-twist spinning system was investigated. The yarns were assessed for different characteristics using objective tests. The results show that yarn hairiness of self-twist yarn increases with the increase of spinning speed and yarn tenacity and extension decrease with increment of spinning speed. The results also show that yarn irregularity, yarn imperfections and yarn twist level have no obvious changes with the increasing in spinning speed. Furthermore, the longitudinal and cross-sectional shape of self-twist yarn were observed and the pictures show that S-twist and Z-twist zone have almost the same structure as the two-plied yarn at ring spinning system and no twist zone has an approximately 45mm length which can influence the strength of the self-twist yarn.