Simulation preassembly based on line feature matching is a preassembly method used for bridge steel components. In this method, components are spliced based on line feature matching of the joint. However, under this method, the overlap rate is not high and the linear accuracy is not considered. Therefore, an improved method aided by design data is proposed herein. First, the reduced bounding box and slicing methods are used to extract the line features of the joint of the components and linear features, respectively. Next, the line features, combined with those extracted from the design data, are fused into the target and source features according to their corresponding relationships. Then, coarse and fine registrations are completed based on point feature histograms and iterative closest point, respectively.Finally, component splicing is conducted using the registration results. The accuracies of the three methods of corner and line feature matching, and the method aided by design data are compared based on simulation data. Results reveal that the method aided by design data can effectively improve linear accuracy. In an actual field experiment, the processing quality of the steel components of the Shanghai Nanheng River Bridge is inspected by line feature matching and the method aided by design data, respectively. The inspection results indicate that the proposed method is practical and can effectively improve the linear accuracy.