The performances of aerostatic spindle are highly affected by thefluid-structure interaction (FSI) between airfilmand solid structure. This paper proposes a novel modeling method to investigate the FSI of aerostatic spindlesystem, by which the structure deformation included by airfilm force can be acquired. Furthermore, a virtualweight loading method is proposed to estimate the stiffness of spindle with consideration of structure deformationand gravitational eccentricity. The reliability of the proposed method is verified by experiments. Based on theproposed FSI model, the influences of airfilm geometrical parameters and structure dimension on the perfor-mance of aerostatic spindle are further investigated and discussed to guide the design of air spindle.