Abstract: A traditional model-updating method can hardly deal with a large complex bridge structural system with multi-degrees of freedom. An important reason is that a structural system is difficult to be accurately represented by the finite element (FE) model coding, and that especially the complete or reduced mass matrix and stiffness matrix are difficult to be built. In this paper, a FE model-updating method based on an application programming interface (API) was developed. An initial FE model was built in Strand7 software, and the physical parameters in Strand7 was rewritten by using MATLAB interactive coding. Thusly, the model can be updated iteratively by MATLAB procedure, and the model updating of large bridge structures was realized. An in-situ bridge was tested by using a multi-reference hammer impact modal test and a truck-load test. The concept of a damage function was introduced to model identification. By comparing between the test data and finite element analysis results, the stiffness of each girder has been identified. Finally, the parameter identification in element level was successfully realized.