Stress/displacement field analyzing of mechanical assembly is important for predicting mechanical property, and optimizing structural parameters and assembly technology parameters of mechanical assembly. However the structural discontinuity and material difference of mechanical assembly determines the complexity of stress function, it is difficult for analytically computing stress/displacement field of mechanical assembly. In this paper, taking bolted joint under the action of normal load as the research object, a stress/displacement field layered mapping and calculating model of mechanical assembly is proposed, with considering the stress/displacement transmission characteristics of mechanical assembly, combining state space method and elastic mechanics theory. The model divides mechanical assembly as the layered structures, and determines layered constraint conditions according to structural discontinuity or continuity in different positions, such as the structure at the junction surfaces is discontinuous. Considering the difference between bolted joint and the common axsymmetric structure, taking the stresses , and the displacements , as the state variables, the state equations based on Fourier-Bessel series was built to express the stress/displacement transmission relationships. Linearizing the stress/displacement transmission rules, the relationships between state variables at arbitrary and external load were determined by accumulated calculating, and stress/displacement characteristics at arbitrary positions of bolted joint structure were obtained. Finally, the pressure distribution of the bolted joint interface, and stress/ displacement distribution of the whole bolted joint structure was calculated, the comparison among the analytically calculation, FEA and the test data proves the effectiveness of the model.