In cross-flow water turbines, the flow channel between the lower nozzle wall and the guide vane acts as a diffuser for partial load operation with a small guide vane opening. Energy loss occurs here due to flow separation and increasing turbulence. The turbine cannot be applied for high heads because an increase in flow velocity causes cavitation below the guide vane. Therefore, the authors propose an energy loss suppression method that consists of sucking air through a hole on the lower nozzle wall upstream of the diffuser. This study is focused on the air intake method's effect at various guide vane opening ratios of the cross-flow turbine via computational fluid dynamics simulations.