This paper deals with a theoretical stability analysis of a self-excited vibration generated in a film wrapped around an air-turn bar. In this paper, stability of the low-frequency mode is examined theoretically. A theoretical model of the film wrapped around the air-turn bar is developed. Basic equations of the air flow in the gap between the film and air-turn bar, and pressurized air flow inside the air-turn bar are derived. The characteristics equation of the system is derived from the basic equations of motion of the film coupled with the air flow. Instability condition is shown as a function of air flow rate and tensile force. Moreover, instability mechanism of the self-excited vibration is discussed based on the theoretical model.