Abstract: The mechanical properties(action stretch,elastic recovery and creeping) of four kinds of PTT staple yarns with twist factor of 280,320,360,400 respectively were studied.Action stretch experiments of the yarns were performed and it was found that the critical twist factor of PTT staple yarn was around 360. Its good elastic recovery was demonstrated by constant rate of extension test and creep test showed that twist factor has insignificant effect on its elastic recovery.The creeping property of the yarn was analogized by a four-element analogous model and the result obtained is coincident with that of the experiment.