The vibration of tube bundles caused by fluid crossflow is a significant cause of damage to the heat transfer tubes in helical coil once-through steam generators (HCOTSG). Studying the flow-induced vibration characteristics of helical tube bundles is crucial for the design of HCOTSG. In practical engineering problems, due to the interactions between tubes in multi-row bundles, their vibration response differs considerably from that of single-row bundles. This paper investigates the differences in the flow-induced vibration characteristics between single-row and multi-row helical tube bundles under the influence of lead–bismuth fluid. Using the Ansys Workbench, combining Computational fluid mechanics (CFD) and Computational structural mechanics, to perform 2-way fluid–structure interaction (FSI) simulations on single-row triple-column and triple-row triple-column helical tube bundle models. By analyzing the fluid field and structural vibration responses, a comparative study of the flow-induced vibration characteristics of single and multi-row tube bundles is conducted. The results indicate that in multi-row tube bundles, in addition to the direct influence of fluid excitation on the tube bundle itself, the rear rows are also affected by the wake turbulence from the front rows. The mutual interactions between tube bundles are more intense, making the vibration responses of multi-row bundles more complex compared to single-row bundles. The amplitude and frequency responses of each row of tubes also exhibit distinct variations. The research on the above issues can provide some references for the study of flow-induced vibration characteristics of helical tube bundles.