Abstarct: One of the main equipment in the power industry that is capable of producing high power rates in limited volume is the gas turbine. Slight increase in the efficiency of these devices also saves a lot on fossil fuel consumption. One of the ways to increase the thermal efficiency and output power of gas turbines is to increase the inlet fluid temperature to the turbine, but it also increases heat transfer to the turbine blades. Since turbine blades are damaged at temperatures above the permissible temperature of the blade mextal, coolling the turbine blades is very important. Therefore, this thesis discusses the cooling of turbine blades. One of the most common methods for turbine blade cooling is the use of ribs to increase turbulence and increase heat transfer in internal cooling channels. In this study, a cooling channel with highblockage ratio (the rib height to the channel hydraulic diameter) which has square ribs in the upper and lower walls is first investigated. Two symmetrical and staggered arrangements are considered for the ribs. To solve the turbulent flow, large eddy simulation (LES) is used. In this simulation the flow is considered transient and the solution is performed at different Reynolds numbers. In continue, bootshape ribs perpendicular to flow (90 degrees angle) with two symmetrical and staggered arrangements is used in the channel. Examination of the flow lines indicates that a recirculating zone is formed downstram the rib which plays a significant role in heat transfer. The values of local Nusselt and mean Nusselt on the down wall in symmetric arrangement are about twice that of staggered arrangement. But the dimensionless average coefficient of friction for the symmetric arrangement is about three times the staggered arrangement. The results show that the use of bootshape ribs increases the heat transfer. Also, the hydraulic thermal performance of the staggered arrangement is between 17% to 29% higher than the symmetrical arrangement.