The thermal hydraulic behavior of the spent fuel in dry storage cask under forced convection mode is experimentally and numerically investigated. For this purpose a test rig is designed and constricted to simulate the cooling loop cask contains 21 spent fuel discharged from pressurized water reactor (PWR). A numerical simulation is performed by ANSYS-CFX fluid dynamic code. The effect of decay heat generation and inlet air velocity are investigated. The results show that the increase in the inlet air velocity improves the coolability of the fuel while the increase in decay heat leads to decrease the coolability of the fuel. Within the range (1.1< V < 2.8 m/s) for inlet air velocity and heaters power (630 < Q < 1260 watt), a new empirical correlation has been obtained for Nusselt number, Nu as a function in Reynolds number, Re. The comparisons between experimental and numerical results show a good agreement.