Cross flow fan has various kinds of performance curves according to housing geometry, but quantitative relations between them have not been made clear. In this paper, experiments are carried out systematically with the housings of simplified form at first. However, the following results are valid even for housings of a more generalized form. It is found that the main geometrical parameters of housing, which determine the fan performance are the tip clearance of tongue, the setting angle of its suction side and the size of casing. the delivery angle of impeller and the height of fan outlet have only a secondary effect compared with these main parameters. The tip clearance is important for the stability of performance curve, and the setting angle has a certain optimum value. Various types of performance curves are obtained by changing the size of casing.