Abstract: The eastern Nanjing interconnecting Bridges of the Shanghai-Nanjing Expressway are all on horixontal or vertical curves. The superstructure of these bridges is constructed with continuous box beams. In order to reach the required road alignment and guarantee the engineering quality the box beams were positioned through the points on the bridge centerline and the points on the cross section. This paper gives the method of coordinate and altitude computation of various points. The related error of computation is also discussed.