Abstract: According to the provisions of the Chinese Code for Seismic Design of Buildings (GB 50011-2010), the anti-seismic capability of a frame structure in two horizontal directions are designed respectively. However, earthquake action is multi-dimensional and random, which will make a panel zone in a frame structure be loaded by bidirectional actions at the same time. Thusly, its anti-seismic capability may be lower than the designed capability based on a unidirectional earthquake action. So far, the detailed calculation methods of shear capability for a panel zone in a reinforced concrete (RC) frame subjected to bidirectional loading have not been reported. In this work, the shear mechanism of a panel zone in a RC frame under bidirectional loading was analyzed. It demonstrated that a synthetic shear force is imposed on a panel zone, the oblique compression zone comes into being at the end of a panel zone, and the diagonal strut is formed in a panel zone, which is different from the shear mechanism under unidirectional loading. A shear capacity calculation model was established based on the strut and tie model, and the predicted values by this work are in a good agreement with the reported experimental results.