Abstract: Based on the analysis of geometric characteristics and location characteristics of the positioning pin holes of the fuel-assembly header,and combined with the visual measurement characteristics of the fuel-assembly header,non-contact precision measurement method can be proposed.The method uses an optical camera to capture the edge image of positioning pin holes.Then the error points of the edge points are removed,and the diameters and their relative position of the pin holes by coordinate values arc fitting of the edge points can be obtained.The detection accuracy of the method is up to 5μm,and in this way can reduce the human measurement error and avoid damage ferrule caused by the contact measurement.Actual operation results show the higher detection accuracy and stability of this method.