Spacer grid is an important component in PWR fuel assemblies for its significant influence on thermal-hydraulic characteristics of the reactor core. In this study, single-phase CFD technology is used to study the flow and resistance in a 5×5 rod bundle with spacer grid. CFX 12 is chosen as the tool software. The geometries of spacer grid and rod bundle are finished by UG code. To simulate the contact of springs and dimples with fuel rods, small gaskets are induced. The SST model is chosen for turbulent simulation. The results of resistance coefficients including both local loss coefficients and frictional loss coefficients under different Re numbers are conformed well to the experiment. The agreement of calculated liquid velocity distribution downstream the spacer grid with the experiment is also well but less satisfactory. We draw attention to the influence of mixing vanes and find that mixing vanes are the main components that induce the lateral flow, but take up little percents in the local loss coefficient of spacer grid. The lateral flow caused by mixing vanes will increase the frictional loss coefficient downstream the spacer grid. These results are beneficial to the optimization design of spacer grid.