Abstract: Numerical technology is used to study the resistance performance of a 5×5 fuel rod bundle with spacer grid. In the progress of spacer grid’s CFD evaluation, we decrease the heights of springs and dimples to leave a small gap between springs, dimples and fuel rods as many researchers do. We use this kind of simplified geometry model to perform numerical simulations, finding that the local loss coefficient calculated is conspicuously smaller than experiments. We improve the geometry model after analyzing the causes and use different turbulence models to simulate the flow, finding that the results got by SST model match the best with that from experiments. We also split the spacer grid into two parts, to model the mixing vanes and other parts separately. The results indicate that the local loss coefficient of mixing vanes takes a little proportion of the total spacer grid. However, the cross-flow initiated by mixing vanes will increase the resistance loss downstream the spacer grid.