The light-gauge tube truss beam is formed by connecting the upper chord, the lower chord, and the Z clip through screws. The failure of the tube truss beam is mainly due to the local buckling of the upper chord, not the tensile yielding of the lower chord. In order to make full use of the material, reduce project costs and manufacture the lower lord more easily, a new type of tube truss beam with U-shaped lower chord is proposed in this paper. Firstly, three tube truss beams with different forms of the lower chord are tested, the effect of upper and lower chord section form, sectional area and stiffness on failure mode, bending stiffness and ultimate bearing capacity of the whole truss beam are examined. Secondly, the finite element analyses of six tube truss beams are carried out, considering different section forms, sectional areas and opening directions of the lower chord. Testing and finite element analysis results have verified the feasibility of using the U shaped lower chord,and the normal U shaped section is better than an upside down one.