The study of the damage mechanism of bridges is an important procedure that turns seismic damage investigation results into a practical technology. The damage features of arch bridges during the Wenchuan earthquake of 2008 differ from those of other earthquakes. Based on the data collected from the Wenchuan earthquake, the seismic damage mechanism of the Jinhua bridge was studied through post-earthquake investigation and numerical analysis. From the site-damage survey, it was found that the Jinhua bridge damage was mainly concentrated in the main rib and arch column, showing mainly concrete cracking and ring cracks of the arch column. The damage mechanism of the rib arch and arch column was simulated by FEM analysis, and the simulation results showed that under seismic loads, the flexural capacity of the spring cross-section of the main rib arch did not meet seismic requirements, while that of the vault cross-section did meet the requirements; flexural cracking appeared at the bottom section of the 8^# arch column. It was concluded that the simulation results agreed well with post-earthquake investigation, and they can provide references for the seismic design of long-span arch bridges in mountainous areas with higher intensity. This paper also proposes some countermeasures for bridge design and construction techniques to minimize typical earthquake damage, and hopes to provide references for future bridge construction.