Bolt interface’s characteristics that existed in aerostatic bearing were affected by many factors,such as part’s material of interface,surface topography,geometric accuracy of interface,interface connect forms and so on. The most important factor was bolt preload force. The characteristics of bolt interface were identified by finite element method（ FEM） and experimental modal analysis method. The influence of bolt preload force on bolt interface’s characteristics was analyzed. Two lows were concluded. Firstly,eigen frequency of interface increased with the increase of bolt preload force. Secondly,bolt interface could be counted as bonded interface in finite element emulation analysis,when the bolt preload force increased to a certain value.