Abstract: Grid is an important part of fuel assembly, making up of the contour of fuel assembly together with up nozzle and bottom nozzle. In order to reduce the hang-up risk of fuel assemblies during handling, the guide vanes have been set on outer strap, which is an important advance in the structural design of grids. Focused on the hydraulic environment of fuel assemblies in the core, considering the possible transmutation of outer strap caused by the lateral hydraulic force chronically acting on grid during operation, the hydraulic force on outer strap of grid is studied with CFD method in this paper.Further research and scheme design are also conducted to reduce the force on outer strap. The results show that the pressure difference between two sides of outer strap will be reduced effectively with the holes set in outer strap, and the effect will be more prominent as the holes move downstream. Meanwhile, increasing the size of holes will also further reduce the pressure difference. Moving the holes to dimples will further balance the pressure between two sides of outer strap, that is, the design of dimples with holes will lower the hydraulic force on outer strap in a greater extent. It is positive to reduce the transmutation of outer strap caused by hydraulic force with the designs above. Thereby, the hang-up risk of fuel assemblies will be reduced during refueling.