Abstract: In order to study the seismic performance and stress mechanism of inner sleeve splicing joints of modular steel construction, based on the experimental study on the seismic performance of the inner sleeve splicing joints, a finite element analysis model with the same size and load conditions as the test joint specimens was established, and the validity of the finite element model was verified. By changing the structural parameters of the joint, the influence of the length of the inner sleeve, the height of the inner sleeve, and the inner partition of the column on the seismic performance of the joint was studied. The calculation formula of the contact force between the inner sleeve and the column wall under the action of axial compression was derived, and compared with the finite element calculation results, the validity of the theoretical calculation formula of the contact force was proved. The results showed that the established finite element model could effectively simulate the working state and ultimate bearing capacity of the inner sleeve splicing joints. The inner sleeve splicing joints had good seismic performance, and the stress state of the joint could be improved by reasonable construction, which could promote the plastic hinge of the beam end to move outward to realize the ductile failure of the joint. Increasing the thickness of the inner sleeve and the length of the inner sleeve had no obvious effect on the bearing capacity of the joint. The setting of inner clapboard could significantly improve the bearing capacity and energy dissipation capacity of the joint. The contact force between the bending deformation of the steel tube column and the inner sleeve increased the stress of the column section under the original load state and produces local stress concentration, the adverse effects should be considered in the design.