Damaged steel connection is usually the leading cause inducing steel structure related accidents. It is more scientific and reasonable to analyze damage of steel and steel connections in micromechanical perspective. Gurson-TvergaardNeedleman (GTN) mode is the most widely applied micromechanical damage model currently;​ however, it has not been promoted in construction field. Therefore, this study attempts introducing GTN micromechanical damage model into study of mechanical performance of building steels. Test specimen taken from Q354 low alloy steels and austenitic 304 hot rolling stainless steel tubes are processed into smooth and notch specimen and then unidirectional tensile test is performed to identify material and damage parameter of two different steel materials. Comparing results with numerical stimulation results, we find GTN damage model is able to accurately predict breaking point of Q345 low alloy steel specimen, but the GTN damage model constructed based on stress-strain relationship stimulated by Ramberg-Osgood curve cannot predict mechanical behaviors of austenitic 304 stainless steels.