Abstract: To inspect the defects on the screw hole surfaces of nuclear reactor pressure vessel in nuclear power station, an automatic moving table was designed to carry sophisticated inspecting devices. Its precise positioningwas successfully realized by determining the positionsof the screw holes in the flange of the pressure vesselwith two optical sensors. Its positioning precision is 0. 15 mm, in accordancewith the design requiremen,t and themoving table has been put into operationwith precise and stable performances.