Dynamic traffic load is a primary cause of damage and failure in bridge expansion joints, influencing not only the service performance of bridges but also potentially leading to traffic safety accidents on bridge decks. This study conducts a vibration response analysis of bridge modular expansion joint (MEJ) under vehicle load. Initially, the working principle, force transmission path, and boundary constraints of MEJs are analyzed to elucidate the factors influencing the vibration response and its characteristics. Subsequently, utilizing ANSYS finite element (FE) software and the APDL parametric modeling technique, a full-scale three-dimensional solid impact vibration analysis model of the MEJs is established. Then, the size, position, and duration of the dynamic traffic load on the expansion device during service are analyzed to achieve a reasonable simulation of dynamic traffic load in the FE model. Ultimately, the dynamic response of the MEJ under typical vehicle load is calculated, and the force state and vibration response characteristics of the expansion joint device are analyzed and discussed. The research methods and findings presented in this paper offer substantial theoretical calculation support for damage identification, condition assessment, and safety evaluation of MEJs.