Abstract: Temperature is the key factor which affects the crimp appearance of PET/PTT filament.The effect of temperature on the structures and properties of PET/PTT filament is studied.The results indicate that the crimp shrinking rate of PET/PTT fiber increases and the crimp elongation rate decreases with temperature rising. No matter under dry or wet thermal conditions,the increasing of temperature accelerates the orientation of the fibers;the sonic orientation factors of both two monocomponent fibers and PET/PTT bicomponent fiber decrease,especially,the PET/PTT bicomponent fiber;also,the crystallinities of the two monocomponent fiber increase while the crystallinity of bicomponent fiber decreases significantly.Decrease in crystallinity leads to the rapid decrease of fiber orientation factor and makes the length of the fiber shrink.The shrinkage rate from disorientation increases and the crimp shrinkage resulted from the shrinkage differential of two components decreases.