In the present study, the interaction between Turgo turbine and water flow was simulated using 2D immersed boundary method. For this purpose, the available computer code was validated by some reliable results of numerical fluid - structure interaction study. Due to the complexity of modeling whole turbine and its details, only the part of Turgo turbine involving three blades was simulated and the obtained results of study was generalized to whole turbine. In order to increase the efficiency of Turgo turbine and obtain the optimal design criteria, different parameters of its components including the concavity of turbine blade, turbine water head, water discharge and the number of blades were investigated. The optimal value of each parameter is obtained according to efficiency values of turbine. Finally, the optimal values of mentioned parameters were used to propose some optimal pattern for the design of Turgo turbine. Also, the results of the analysis showed that the immersed boundary method despite having simple formulation and algorithm can be utilized to provide a reliable numerical solution to simulate interaction between the parts of turbine and water flow.