Abstract: To study the effect of high temperature on the moment-rotation relation and failure mode of extended endplate connections between square tubular columns and steel beams, a finite element model (FEM) of a typed joint at high temperature was proposed by using ABAQUS software. The nonlinear full process analysis was made at high temperature. The influence of parameters on the moment-rotational relation of the connections at various temperatures was studied. It was concluded that: the endplate width, column compressive ratio, bolt diameter, steel strength, and tube thickness obviously affect the connection moment capacities at high temperature; the endplate width, the bolt diameter, the steel strength, and the tube thickness also affect the connection rotational stiffness at high temperature. The connection moment capacity and stiffness were high and failure region was only in the compressive beam flange; the connection moment capacity and stiffness decreased with temperature and failure region moved to the joint core; the failure region was developed into the tube column when temperature was beyond 500℃.