In the high-pressure gas-turbines, with hot-flowing gas through the stator channels with a high mass-flow rate, even slight variation in the blade geometry will have significant effects on the downstream flow-field. These minor changes can be compared to corrosion rates. The first occurrence of this corrosion is the non-uniformity of flow in the stator-rotor axial distance. This non-uniform flow, due to the complex pattern of vortices, prevents the complete transfer of fluid energy to the rotor and greatly reduces the turbine performance. In this research, a high-pressure turbine is considered to be at high risk of corrosion. The main goal is to predict these variations due to corrosion. Firstly, a 3D numerical analysis of the turbine initial model was conducted to accurately observe the flow field and the results were validated by the existing experimental results. Then, in order to investigate the effects of corrosion on the turbin performance, the blades geometrical changes were applied in stator blade profile and the flow distribution was analyzed. Results show that the highest corrosion risk is at the trailing-edge of the blades. Due to reduction in the stator inlet-outlet area ratio, the axial-velocity is reduced. But simultaneously, with increasing the stator channels outlet area, the mass-flow rate is increased by 7.31%. Therefore, the turbine undergoes to an off-design condition. The flow pattern will be more complicated in the rotor's entrance, and corrosion will develop rapidly due to temperature rise as the flow separates from the rotor blades.