Rivers Water currents or flow in canals are considered as reliable source of power generation. Savonius rotors are considered suitable for power generation from water current. In this paper, an attempt has been made to develop a multi stage rotor with variable diameter of Savonius turbine in order to enhance the performance of Savonius rotor. This innovative multi stage Savonius rotor has been numerically investigated using commercially available ANSYS FLUENT code. A three stage Savonius hydrokinetic turbine with variable diameter in each stage has been designed and developed. SST k - ω turbulence model in addition with VOF-open channel flow model has been applied in order to simulate the performance of Savonius hydrokinetic turbine in open channel flow. Based on simulation results, power coefficient has been found to be maximum as 0.32 at TSR of 0.8.