The effect of draw ratio and take-up velocity on the structure and property of the ultra-fine denier PET full drawing yarn (PET-FDY) with monofilament linear density equal to 0.38dTex was studied in this paper. The crystalline structure and crystalline size were determined by XRD method and size was reduced with increase of draw ratio. The orientation of whole molecular chain was determined using sonic velocity method. The mechanical properties and boiling water shrinkage were also examined. Draw ratio had greater influence on the boiling water shrinkage than take-up velocity did.