Abstract—The Stress-weighted Damage Model (SWDM) based on microscopic fracture mechanism can be used to predict the ductile fracture of steel by considering the influence of lode angle parameters and stress triaxiality. However, the calibration work of undetermined parameters of this model is not perfect, especially for Q420C steel is rarely reported. In addition, the fracture analysis using the microscopic fracture mechanism model is still mainly focused on simple structure, and the analysis of complex joint is rarely reported. In this study, the parameters of SWDM model of Q420C and Q355B steel were calibrated through the material test and finite element analysis. The constitutive model based on SWDM was realized by ANSYS program, and the influence of model mesh size was considered. Then, the fracture analysis of a new type KT joint with both tube-gusset and intersecting connections was carried out. The analysis results show that for the connecting plate of the oblique branch pipe of the joint, the cracks first appear at the end of the connecting plate on the outside and the edge of the ring plate, then the cracks gradually expand and connect with the cracks near the bolt holes. Finally, the cracks extend to the horizontal circular pipe and tear the connecting plate from the horizontal circular pipe. In the process of loading, the influence of horizontal and vertical circular pipe axial force on the ultimate bearing capacity of inclined branch pipe is only 4%, which is relatively limited. In addition, the bearing capacity of the node can still be increased by about 16% after the crack appears, which means that the joint has great guarantee of security.