This study aimed to determine the effect of adding the sluice gate and the optimal width of the sluice gate on the waterwheel performance. Tests have been carried out experimentally on a laboratory scale. In the test, this study used an open channel waterwheel with variations in the flow gap width gate width of 25mm, 35mm, and 40mm. Each variation of the flow gap width will be tested at a flow rate of 12 liters/second. Parameters such as mill power, turbine torque, and efficiency will be determined based on the measurement results of the rotational speed of the waterwheel wheel, water level, and braking load. The results showed that the width of the sluice gate flow gap affects the performance of the waterwheel. The highest performance was obtained at a flow gap of 25mm followed by a flow gap width of 35mm, and the lowest performance was obtained at a variation of the slit width of 40mm. The maximum performance of the waterwheel is obtained at variations in the width of the flow gap of 25mm at 50 rpm rotation conditions with a discharge of 12 liters/second where liters were generated 15.06 watts and the efficiency 29.82%.