As a typical semi-rigid connection method, the extended end-plate connection of steel frame beam-column has complex mechanical properties. In order to fully understand the force characteristics of the connection mode, ANSYS Workbench software is used to establish a finite element analysis model, and the mechanical performance of the connection joint under the action of high-strength bolt preload and vertical displacement load is analyzed under the consideration of material nonlinearity, geometric nonlinearity and state (contact) nonlinearity. The results show that: 1) Under the action of preload, the contact pressure between the bolt and the end-plate is concentrated around the bolt hole, and the distribution area is about 10 times of the cross-sectional area of the bolt rod; 2) Setting the column web stiffener and the end-plate stiffener is an indispensable structural measure for the extended end-plate connection joint; 3) The high-strength bolt in the tension zone is subjected to greater tensile and shear force, and the bolt in the compression zone will also bear greater shear force in the elastoplastic stage. The results can provide some references for the analysis and design of steel frame beam-column extended end-plate connection.