The structural behavior of X-joints between rectangular hollow sections is simulated with FEM(finite elements method). The strength of joints calculated with FEM shows a reasonable good agreement with the test results and the design strength equations derived from simplified yield line models. The strength of X-joints under combined loads, axial loading and bending moment is also investigated with FEM. The results analysized with FEM show higher strengths than the values estimated by the linear interaction diagram which is generally used for design.