To study the effect of the stiffening plates between brace and chord and the width ratio of brace section to chord section on failure mode, bearing capacity, and distribution and evolution of stress and strain in connection zone of T-joints of lightweight aggregate (LWA) concrete-filled high strength steel square tube truss, static loading tests under axial compression on brace were performed on T-joint with stiffening plates and traditional T-joint. Tests results show that typical failure modes of T-joints of LWA concrete-filled high strength steel square tube truss included concave of top flange of chord in connection zone, convex of chord webs, bending of chord, lateral instability of brace, buckling of stiffening plates, crack of weld between chord and brace, and crack of weld between stiffening plates and brace. The bearing capacity of the traditional T-joint depended on the compressive strength of brace root and its welds and the local compression zone of top flange of chord in connection zone, and there was a flow-plastic platform in the load-displacement curve of the traditional T-joint. The bearing capacity of the stiffened T-joints depended on the compressive strength of brace root and its welds, the diffusion compression zone of top flange of chord in connection zone, and the buckling strength of stiffening plate. The load-displacement curves of the stiffened T-joint showed gradual upward trend without flow-plastic platform. The bearing capacity of the T-joints was obviously improved by the stiffening plates. The yield load and ultimate bearing capacity of the stiffened joints increased by 10.0%-40.0% and 15.0%-48.3% compared with those of the traditional T-joint, respectively. The yield load and ultimate bearing capacity of the stiffened joints increased with the increase of the width ratio of brace section to chord section.