This paper uses a three-point bending test to investigate the influence of aluminium tube cross-section shape and thin-wall thickness on mechanical behaviour. Four cross-section structures are studied through the finite element modelling method: hollow circular structure, circular cross support structure, hollow rectangular structure, and embedded double-layer rectangular structure. The effect of wall thickness is simulated under three-point bending loading, which is 1.0, 1.5, and 2.0 mm. The load-displacement curve, fracture failure behaviour, and Mises stress cloud diagram were obtained, the comparison between different structures and wall thicknesses was carried out, and directional suggestions were put forward for further research. The results were shown that the second structure has a higher peak load and energy absorption efficiency and good comprehensive mechanical properties. With increasing thickness, four cross-section aluminium tubes can provide better-bending properties.