Abstract: The distribution and causes of ramie yarn hairiness were analyzed.The traditional methods of reducing ramie yarn hairiness and their disadvantages were given.To eliminate ramie yarn hairiness in warp sizing,lateral twist auxiliary device based on false-twisting was designed,by which,the ramie yarns were sized.And the mechanism of lateral twist auxiliary device was discussed.Ramie yarns sized by lateral twist auxiliary device and ordinary auxiliary device respectively were used to weave samples separately,and the two samples were compared for the sizing quality.The results showed that the content of ramie yarn hairiness by this device was reduced by 90%.The yarn quality was improved obviously,the opening in weaving process was clear and the end breaking rate decreased sharply.