Abstract: To understand thoroughly the effect of the column web stiffener of extended end-plate connection on the failure mode in fire and the fire resistance, a nonlinear finite element analysis is performed. For the column web without stiffener, the plastic strains in both tension and compression areas in the web increase with the elevation of temperature, and a plastic hinge is formed finally, resulting in the buckling of the column. If the column web has only compressive stiffener, the yielding of tension area in the web leads to the column buckling and the joint failure. For the column web with both tension and compression stiffeners, the plastic hinge line produced in tension area of the endplate causes the endplate to be apart from the column flange, which leads to a large rotation of the beam and local buckling of the compressive flange of beam at last, thermal axial force in the beam decrease. Smaller thermal axial force in the beam is helpful for the stability of the column and whole frame in fire.