In order to solve the insufficient bearing capacity of the large-diameter circular steel tube K-Joints, the chord in the joint zone is filled with the concrete. The reinforcement of bearing capacity that the concrete makes to K-Joints is researched with the finite element numerical simulation method, in consideration of the material nonlinearity and the geometric nonlinearity. The numerical computation of bearing behavior is employed to eighteen groups of the large-diameter circular steel tube K-Joints and reinforced ones with the concrete (RK-Joints). The failure styles and the influencing factors of bearing capacity are analyzed with RK-Joints. The result shows that the bearing capacity of K-Joints is enhanced significantly by the concrete filled in the chord in the joint zone. The load-deformation curves reveal the changing regularity that the bearing capacity of joint follows the relevant parameters. It can provide reference for the engineering application of RK-Joints.