It is necessary to supply air into a runner chamber of a cross-flow turbine installed with a draft tube, which is different from any other types of water turbines. Turbine efficiency changes depending on the supplied air flow rate, and therefore, the efficiency calculation becomes more complicated than that of the other water turbines. Since turbine performance is largely influenced by the behavior of air volume, it is still difficult to predict overall performance from each component performance. Here we propose an effective head and recirculation loss by which the overall performance of a cross-flow turbine can be predicted for various operating conditions. The hydraulic losses are studied experimentally by changing the position of the installation of the nozzle, the net head and the runner diameter.