Abstract: With a model of bend standing wave of thin plates, under some assumptions, the author analyzes the air squeeze-film damping theoretically and deduces new formulas of loss factor, which include 5 factors:the thickness of air film, the frequency of vibration, the stiffness of the plates, the viscosity and pressure of air. These formulas reveal the feature of air film damping more comprehensively. The values of loss factor calculated for two constructions with the formulas approach to thos measured for similar constructions reported in references.