The K-type tubular joint is one of the most widely used nodes in steel pipe structure engineering because of its simplified intersecting lines and good precision. The investigation on damaged steel structures caused by major earthquakes showed that the design and construction of connection nodes were flawed. Since the node is a key part of the structure and dissipates seismic energy, a research on strengthening the steel structure joint is necessary. The overlapped K-point of a steel tubular section is prone to cause local buckling and tearing on the main tube wall. Herein, a new strengthening K-type joint is proposed; the concrete poured between the main tube and internal tube was used to stiffen the K-joint. Compared with the method of filling concreate in the main tube, this enhanced node can not only keep the building beautiful but also reduce the structural weight. Using the finite element software ANSYS, the ultimate bearing capacity and hysteretic performance of unstiffened and stiffened joints are analyzed. Compared with pre-strengthening nodes, the failure mechanism under static and reciprocating loads is investigated. The results show that a stiffened joint can effectively improve the mode of failure, reduce stress concentration near the joint and enhance rigidity and bearing capacity of the joint. The unreinforced joint shows a complete hysteresis curve; however, when compared with the reinforced joint, the bearing capacity of unreinforced joint is much worse. The ultimate bearing capacity of the joint can gradually increase to reduce the inner tube size. When the inner tube size is reduced to a certain value, the bearing capacity of the node does not change.