Abstract：In order to study diaphragm on the coupling vibration of vehicle-curved bridge system, a finite element model of the bridge and the model of the vehicle moving system were established based on the three-span continuous girder curve bridg. Its cross-section was double-room single box with curvature radius of 250 m. The influence of diaphragm on the mode shape and natural frequency of the bridge was analyzed. Iterative algorithm procedure was used by COMSOL and MATLAB. Dynamic response curve bridge with or without the diaphragm was compared under C-level roughness. The results showed that the natural frequency of each order is reduced due to the diaphragm, particularly for the effect of vertical bending vibration. Under dynamic load, vertical displacement and the torsion angle in each span were reduced due to the diaphragm. The stress in side span was greatly reduced which made the curved bridge more stable. This study provided initial theoretical basis for the structural improvement of new curved bridges, repair and reinforcement of damaged bridges.