In the bridge maintenance industry, the transition of bridge disease detection from traditional mode to digital mode has become the development trend of the industry, and the 3D visualization of bridges is the basis of the realization of digital detection. General beam bridge parameterized modeling program has the disadvantage of "once written, it is not easy to modify". In order to avoid such defects and improve the flexibility and extensibility of parametric modeling, a method combining expert system with parametric modeling of girder bridges is adopted. By combining expert system theory knowledge, beam bridge structure knowledge and parametric modeling process of beam bridge components and whole bridge, this method designs a rapid modeling expert system for beam bridge. The main contents of the system include the classification design of knowledge library, design of database table for knowledge library, the selection of knowledge expression, the reasoning content of component modeling and full bridge modeling, and the algorithm of component, assembly and full bridge modeling in parametric modeling. Finally, through the analysis of the modeling results, it is found that the method can accurately complete the parametric modeling of bridge components and the whole bridge according to a few main parameters given by users. By modifying the knowledge library, users can change the structural calculation knowledge that the parametric modeling process depends on. This method increases the flexibility and extensibility of parametric modeling.