A method for detecting positions of wafers includes: rotating a rotation table with a wafer thereon in a first direction at a first speed; detecting a contour of the wafer rotating in the first direction at the first speed to provide contour data; rotating the rotation table in a second direction at a second speed when an aiming feature of the wafer passes the detector in the first direction at the first speed; detecting the contour of the wafer rotating in the second direction at the second speed to provide new contour data; and stopping the rotation of the rotation table and the detection of the wafer according to an accumulation of contour data and corresponding rotation angles, to estimate an eccentric position of the wafer and a position of the aiming feature when the aiming feature passes the detector in the second direction at the second speed.