Maintenance of existing steel structures has been a hot issue in recent years. A hybrid bridge was created from an original steel structure by integrating with the concrete members. The purpose of the present study is to investigate the mechanical behavior of the renovated girder. Based on the experimental observations, a three-dimensional FE model capable of analyzing these kinds of composite structures was built. Strength and deformation response, sectional strain distribution and movement of composite neutral axis before and after concrete cracking were observed in the test and compared with the numerical results, and the results predicted by this modelling method are in good agreement with those obtained from the tests. Results indicate that the renovated structure can greatly enhance the stiffness and reduce the stress levels, resulting in the extension service life of the structure.