The PET/PTT self-crimp filament appears obvious crimp elasticity under appropriate finishing conditions. The paper discusses the properties and structures of the PET/PTT filament at different temperatures. With the rising treatment temperature, the shrinkage of PET/PTT fiber increases, while its crimp elongation decreases; both the sonic orientation factor of PET/PTT fiber and the crystallinity of PET and PTT component in PET/PTT fiber decrease. The sonic orientation factor of PET fiber and PTT fiber decrease, their crystallinity increases with the rising treatment temperature. The decrease of the crystallinity of two components makes the orientation lower, which leads to the results that the length of the fiber shrinks and the shrinkage is higher than the crimp shrinkage from the shrinkage difference of two components.