During the operation of a Pressurized Water Reactor (PWR), small foreign particles may enter the reactor fuel assembly rod bundle channel through the lower tube seat and become trapped between the grid and the rod bundle under the force of the coolant flow. These trapped particles vibrate due to the coolant’s scouring action, leading to abrasion of the fuel rod cladding surface. Prolonged abrasion can result in fuel cladding damage, potentially causing cladding rupture and radioactive material leakage. Therefore, it is essential to analyze the abrasion behavior of fuel rod cladding caused by foreign particles within the rod bundle channel under high-speed coolant flow. In this study, the behavior of foreign particle-induced abrasion damage is investigated, with a focus on the key factors influencing fuel rod failure. Using fluid–structure coupling numerical analysis, a series of phenomena occurring after foreign particles enter the fuel assembly rod bundle channel are simulated. The influence mechanisms of different boundary conditions and particle types on cladding abrasion damage are explored. Key parameters, such as the motion state of foreign particles and the physical properties of the flow field, are obtained, and the abrasion volume is quantified. This study provides a theoretical analysis method for understanding foreign object motion in PWRs and offers support for the safety evaluation and optimal design of fuel rod cladding.