In order to investigate the effect of the stiffening structure on the failure mechanism and bearing capacity of the N-type joint, static loading tests under axial compression on brace were performed on strengthened joints and basic joint. The test results show that the failure mode of the basic joint is the buckling of the upper flange of chord, while the failure mode of the reinforced joints are the buckling of the stiffened ribs and the cracking of the weld between cover plate and flange of chord. The bearing capacity of the strengthened joint increases by 9.4%~36.5% compared with that of the basic joint. Increasing the thickness of the cover plate can obviously improve the bearing capacity of the gap N-joint. The finite element parameter study of the gap N-joints of Q460C steel square tube reinforced by clover plate and stiffening ribs was carried out by using ABAQUS software. The effects of the ratio of width to thickness of chords, γ, the ratio of the thickness of chord to brace, η, the ratio of the width of chord to brace, β, the angle between tensile brace and chord, θ, the ratio of the gap between two braces to the width of chord, ξ, on failure mode of gap N-joints, stress distribution, load-displacement curve of chord and fracture index, I_f of fillet weld between cover plate and chord flange were investigated. Based on the results of experiment and numerical simulation, the formula of bearing capacity calculation for the gap N-joints of Q460C steel square tube strengthened with cover plate and stiffening ribs was derived and the structural design suggestions were put forward.