Abstract: Existing cracks in RC structure influence the formation and propagation of new cracks, thus affect the behavior of the whole structure. Experiments on RC beams with regular hexagon cross section were carried out to study the mechanism of multi-directional cracking and its influence on the bearing capacity. Five-stage loading was applied. Bending cracks were designed to occur during the first 2 stages, penetrating the swhole cross section, then, changing loading condition, diagonal shear cracks were designed to cross the existing bending cracks during the next three stages. Multi-directional Crack propagations were observed, and reaction-displacement curves were recorded in experiments. The mechanism of 3D multi-directional cracking and its influence on bearing capacity were discussed, and a 3D fixed multi-crack model was developed. Adopting the newly developed model, a finite element analysis was performed. A comparison between numerical and experimental results shows that this model can be applied to analyze multi-directional cracking.