Considering the nonlinear factors,the contact and friction between plates as well as bolt and plates,bolt preload,etc,three-dimensional finite element model bolted structure was developed. Three mathematical expressions of contact stress was deduced,which was based on the assumption that stress distribution in a circular cone. Compared with the finite element analysis,the corresponding deviation is within 9. 2%; Based on finite element computation,The influence to contact stress between connected components was analyzed with different thickness of the connected component,the clearance of the bolt hole and the diameter of nut. the experience formula of the connection stiffness was got,compared with the finite element analysis,the deviation of obtained member stiffness less than 5. 24%.