The potential of water power is spread throughout Indonesia. The velocity of river flows in Indonesia is relatively low with an average of 0.6 m/s. With a low water velocity, a vertical axis turbine is used for better efficiency values and maximized blade's lift by using twisting. In this study using vertical axis helical turbines with overlapping variations. Helical savonius turbine with a 45o twist and 3 blades are designed to improve turbine performance. This study compares the horizontal axis helical savonius river current with variations in the overlap ratio of 0.1, 0.2, 0.3, and 0.4. Validation of turbine design was done by simulation using fluent software to determine numerical analysis and best performance. The simulation was performed on ANSYS 19.2 with standard k-epsilon modeling and SIMPLEC algorithm. From the simulation results obtained overlap ratio 0.1 had the most maximal turbine performance compared to other overlap variations due to the greatest pressure and velocity difference and the greatest coefficient of torque value.