Blasting excavation is a critical construction method for enhancing the canal channel expansion efficiency. However, the induced blasting vibration may adversely affect the substructure of existing waterway bridges. To clarify the dynamic response characteristics of the bridge substructure subjected to blasting-induced vibration, this study analyzed the stress and vibration velocity distributions in the adjacent bridge substructure during the Pinglu Canal channel expansion project. A finite element numerical simulation method, validated by field test, was employed to establish the safe vibration velocity threshold for the substructure based on the maximum tensile stress criterion. The results show that the maximum tensile stress occurs at the interface between the bridge pile foundation and the pile cap during canal blasting excavation. The most significant vibrations in the substructure are concentrated in the pile foundation. The allowable vibration velocity for the bridge substructure, with the pile cap as the monitoring point, is 3.2 cm/s.