Effects of geometrical changes (due to twist, lean and bow) for the second stage blade of Avon gas turbine on the turbine performance have been studied. At first, a 3-D approach for gas turbine simulation has been validated by using experimental results for one stage of Hanover turbine. Then, second stage of Avon turbine was modeled with this numerical method and the results were validated by performance data of this turbine. In the next step, geometrical changes for second stage rotor of Avon turbine were applied on turbine geometry and flow and temperature fields due to these changes were simulated with numerical softwares. Finally, effects of these changes on performance of the second stage (efficiency, pressure ratio etc.) were evaluated. In this study, the geometry changes including lean, bow and stagger angle of the blades were investigated. Finally it was observed that changing blades stagger angle caused the mass flow rate to change greatly. This factor will lead to changes in the turbine power. Lean and bow effects on the performance of turbine are Negligible.