Abstract: Fluid-structure interaction simulation is an important research content of reactor numerical simulation. Based on the characteristics of thermal hydraulic software PACA and structural mechanic software HARSA of CVR1.0 (China virtual reactor), mesh mismatch, huge number of mesh and difficult to restore mesh cells, 3D-R tree was used to index large-scale fluid domain mesh nodes to complete the interpolation calculation of solid domain mesh nodes. In view of the high density and relatively uniform distribution of fluid domain mesh nodes, a new node splitting strategy of 3D-R tree was designed by using volume averaging method. In the new strategy, for the overflow node, the best split axis will be calculated firstly, and the best split axis can ensure that the sum of the new nodes volumes after splitting is the smallest, assuming that it is the x-axis. The node is divided equally by the split plane perpendicular to the x-axis. Child on the left of the split plane is inserted into new node N₁, child on the right of the plane is inserted into N₂, and other nodes are inserted into N₁ or N₂ with the smallest increasing volume. The interpolation efficiency is verified by PACA and HARSA. Experiments show that the interpolation efficiency of the improved 3D-R tree is significantly higher than that of the 3D-R tree and traditional interpolation method. Furthermore, HARSA was used to calculate the solid flow-induced vibration, and Archard model was used to evaluate the solid wear.