Abstract: Unsteady Reyolds Average Navier-Stokes Simulation (URANS) and Large Eddy Simulation (LES) are used to study the flow field of 5×5 rod bundles with split-type spacers. An entire geometry of spacers, including grid straps and split-type vane, is simulated, and the results are compared to the experimental results of MATiS-H. The results show that URANS and LES can predict the averaged value of components of velocity, though there is a little difference between simulations and experiment. For RMS value of components of velocity, Unsteady SST k-(URANS) solution cannot reproduce the pulsation of components of velocity and the pulsation of components of velocity is under predicted by Unsteady RSM (URANS). The result of pulsation of components of velocity can be reproduced by LES while it is under predicted.