Taking the engineering groups built in tidal reaches of the Yongjiang River Basin in Ningbo City as an example, the cumulative influence of bridge and wharf groups on flood propagation under typical flood and tidal conditions was studied based on the numerical model of Delft3D. The results of the influence of a single type and two types of engineering groups on flood level and flow velocity were contrastively analyzed. The results show that bridge and wharf groups have a cumulative influence on flood propagation, which is located in the reaches of the Yongjiang River upstream of Ningbo University, the Fenghua River and the Yao River. In the region of water level (velocity) both increase or decrease by the single type of bridge or wharf groups, the water level (velocity) has a higher variation amplitude by the combined action of bridge and wharf groups, but the changed value is not a simple superposition of the influence amplitude of two engineering groups. In the region of water level (velocity) changes in opposite by the single type of bridge and wharf groups, the variation amplitude of water level (velocity) is reduced by the combined action of bridge and wharf groups.