High-precision prealigner is a crucial component in wafer transport device for modern photolithographer.Firstly,design and realization of a prealigner were presented.A three-freedom-degree prealigner mechanism,including rotation stage,centration stage and lift stage,was illustrated.A CCD sensor with liner array was used to detect the edge of the wafer.Least square circle-fitting algorithm was adopted for positioning the center of the wafer and its notch.Effectiveness of the prealignment method was validated by experiments.Then,control system configuration of the wafer transport device was given,and an approach for re-locating,which was used to calculate the wafer eccentricity,was briefly introduced.Finally,experiments of repetitive precision are carried out and the results show that precision of the wafer transport device can be effectively improved based on the prealigner.