Abstract: The influence of foil predeformation on the static characteristics of bump foil journal bearings was analyzed in this paper.The air film thickness model was developed with considering the air compressibility and foil predeformation.Both finite difference method and Newton-Raphson method were applied to solve coupled Reynolds equation and air film thickness equation.Compared to the bump foil bearings with nominal clearance,air film thickness,pressure distribution and load carry capacity were discussed.The results indicates that the bump foil bearing with predeformation provides a better rotating stability and a greater load carrying capacity,and in some extent the foil predeformation is larger,the load carry capacity is higher.