Complex steel structural members usually require pre-assembly at the manufacturer to ensure the manufacturing quality of the members. The pre-assembly of large components requires a large amount of space and a large amount of manpower, mechanical equipment, auxiliary materials, etc., which greatly increases the production cost of the factory. How to reduce factory production costs by reducing physical pre-assembly in the factory, and ensure the manufacturing quality of components and ensure the smooth progress of on-site construction has become a difficult problem that needs to be effectively solved in the steel structure industry. Digital pre-assembly technology based on three-dimensional scanning recognition and reverse modeling effectively solves this problem and fills the gap in this technology in China. This achievement developed a series of digital pre-assembly software and created a new digital pre-assembly method based on three-dimensional scanning recognition and reverse modeling. It breaks through a series of technical bottlenecks in the process of point cloud processing, reverse modeling and digital pre-assembly caused by the massive amount of point cloud data in three-dimensional scanning, overcomes the problems of difficulty in atomization and boundary identification of three-dimensional scanning point cloud, and forms a new point cloud reverse modeling model, which first reverses modeling and then registers, innovatively proposes a point cloud deformation correction method based on structural mechanics analysis, and takes the lead in realizing the application of three-dimensional scanning and reverse modeling technology in digital pre-assembly of steel structures. Promote the progress of steel structure pre-assembly technology. The main innovation results are as follows: ①. Digital reverse modeling and pre-assembly software for steel structures has been developed, innovatively using three-dimensional scanning technology, reverse modeling technology and simulation pre-assembly technology based on optimization algorithms to realize three-dimensional digital pre-assembly of steel structures.②. A digital inspection and assembly software for steel structures has been developed to realize three-dimensional digital inspection of steel structural members based on the three-dimensional scanning point cloud of components.③. A method of improving scanning clarity by auxiliary markers is proposed. By increasing the intensity contrast of point clouds at boundary positions, the ability of point clouds boundary recognition is improved, which solves the problem of three-dimensional scanning point clouds ldquo; atomization; boundary recognition difficulties and the self-weight deformation of flexible components affecting the accuracy of point clouds lays the foundation for the effective application of point clouds in reverse modeling and digital pre-assembly. Innovatively use structural mechanics methods to calculate component deformation and correct point clouds, improving the accuracy of point clouds. It provides technical support for the review of long-span steel structures after installation.④. A point cloud processing technology based on Tekla model comparison is proposed to increase the accuracy of point cloud processing. We independently developed digital point cloud processing software for steel structures, improving the efficiency of point cloud processing. Digital reverse modeling software for steel structures has been developed. Based on the known characteristics of steel members, a method of ldquo; fitting first and then registering rdquo; is proposed, which solves the problems of low efficiency of manual processing of point clouds and difficulty in fitting steel structures, and provides a guarantee for the efficient creation of reverse models of components.⑤. Creatively proposed a digital pre-assembly method based on three-dimensional scanning with targets, which simplifies the assembly steps, exponentially improves the efficiency of three-dimensional digital assembly, solves the problem of massive point cloud data affecting efficiency, and lays the foundation for the popularization and application of digital pre-assembly. Based on the actual status and needs of my country's steel structure industry, and on the basis of fully drawing on advanced foreign technical means, this project independently developed digital pre-assembly technology can solve the problems encountered when checking complex forms and manufacturing accuracy of massive components. It is of great significance. This technology has been applied in Shaoxing Shanshui Museum, JUMBO in the United States, Nanjing Golden Eagle and other projects, and has produced good economic benefits. This project applied for 5 invention patents and 5 software copyright registrations, and formed 2 technical papers. The overall results of the project have reached the international advanced level. The application of the results can reduce the workload of factory entities, double the efficiency of component inspection, reduce the occupied space, reduce the pressure on construction period, personnel, equipment and cost, and improve the quality of steel structures. It has great application prospects.