During the operation of nuclear power system, foreign objects often intrude into the secondary side of the steam generator (SG), disrupting the flow in the secondary circuit and potentially causing SG tube damage. Therefore, it is crucial to investigate the motion behavior of these foreign objects within the SG's secondary side. Using the computational fluid dynamics and discrete element simulation method (CFD-DEM), this study examines the motion behavior of particles within the fluid field. The bidirectional fluid–solid coupling method is based to build the coupling simulation model between three-dimensional fluid field and foreign object in SG tube section. In the fluid zone, the change of channel will cause irregular motion so that foreign object would collide with the component, resulting in damage of SG tubes and support plates. When foreign object stay in the fluid zone for long, the risk of SG tube damage would grow higher. This study reveals the distribution of foreign objects, identifying high-risk areas prone to damage on the secondary side of the SG tube section. With the qualitative and quantitative analysis to foreign object on the secondary side of SG, this paper will offer the reference and conduction for the overhaul of steam generator.