In order to study static strength of doubler plate reinforced circular hollow section (CHS) K-joints, experimental and numerical studies conducted by the authors. The effects of parameters Δ (the ratio between the length of doubler plate and the diameter of the brace) and α (the width of the doubler plate) on CHS K-joints subjected to bending load have been investigated and reported by the authors. It is found that the ultimate strength of a CHS K-joints reinforced with appropriately proportioned doubler plates can be up to 2 ratio to its un-reinforced counterpart. Reasonable geometric parameters of the doubler plate can make the chord, brace and doubler plate work together to bear the external bending load. The width and length parameter of the doubler plate, however, have no effect on the stiffness of the reinforced K-joints.