Existing theories for 2-dimensional foil sections can predict foil performance in noncavitating condition or sheet cavitation condition, but cannot predict foil performance in bubble/streak cavitation condition. In this study, the authors developed a new method to predict foil performance in bubble cavitation condition theoretically. Displacement thickness due to bubble cavity is calculated by solving Reyleigh-Plesset equation in an iterative method, and pressure distribution around the “displacement body” is computed. Experiments are performed in a cavitation tunnel in order to verify the accuracy of new prediction theory. The calculated results by the new theory agreed well with the experimental results on foil performance. It is still difficult to predict foil performance when sheet cavitation turns into bubble cavitation.