Abstract: In order to study the effect of the plate on the behaviors of extended end plate semi-rigid connections, model doesn't have a plate and have an addition plate of extended end plate semi-rigid connections are simulated by using ANSYS. The finite element results were compared with the existing test result. Moreover, we deeply investigated the effect on the deformation properties of steel frame extended end plate connections semi-rigid joints. The results show that the finite element results of considering the multiple contact relationship which are close to the actual situation between the joint areas are better close to the actual experimental results. The finite element analysis result of the similar moment-rotation curves, hysteretic curves and joint deformations are also consistent with experimental data. Add a thin plate on end plate connections can declined the carrying capacity, but improved its ductility. The bigger ductility has the better warning effect to predict the early damage of structure.