The shroud block is one of the hot components of the gas turbine. Like the blades, various cooling technologies have been applied in the shroud block to protect against high temperature operating conditions. Among them, the impingement jet cooling which is most effective for increasing the heat transfer coefficient has often been used. However, the cooling effect by the impingement jet is not appear to be effective in some shroud block geometries whose H/D is greater than 8. Therefore, in this study we improve the internal heat transfer of the shroud block by modifying the impingement jet shape. All simulations were performed by considering real gas properties of air and by using SST turbulence model and commercial program ANSYS-CFX 17.2. To improve the cooling effect by the impingement jet, the heat transfer is increased by modifying the shape so that the jet core had a H/D of about 4 to 6, which is a range directly affecting the impact surface.