Abstract: Pressure drop of 5×5 rod bundles was conducted with experimental and numerical investigation. An experiment was conducted in the test section within 5×5 rod bundles to obtain the pressure drop. The Reynolds number ranges from 2 000 to 14 000. The relationship between pressure drop and Reynolds number was obtained. The empirical correlation of frictional factor was obtained by test data and the relative deviation between test data and calculated value by empirical correlation is less than 5%. Based on test data, numerical investigation of pressure drop characteristic of 5×5 rod bundles was conducted. To conduct numerical investigation of 5×5 rod bundles, the laminar model was selected for the condition which Reynolds number was less than 2000, and standard k-ε model, Realized k-ε model, RNG k-ε model and LPS-RSM were selected for the condition which Reynolds number was more than 2 000. The empirical correlation in laminar condition was built. The result of numerical investigation using standard k-ε model, Realized k-ε model, RNG k-ε model or LPS-RSM shows reasonable agreement between experiment and simulation in condition of high Reynolds number.