The formula for the bending capacity of aluminum alloy gusset joints loaded by out-plane bending moment was proposed theoretically. The experiments on four aluminum alloy gusset joints, three loaded by out-plane bending moment and one loaded by shear force together with out-plane bending moment, were conducted. The possible failure modes of the gusset joints were presented, which are as follows: member bending failure, joint plate block shear rapture failure and joint plate bucking failure. Based on the test results, the range of k1, which represents the reduction of the bending resistance caused by prying action, was proposed, and the formula for bending capacity was verified. Correspondingly, 4 finite element models were established by finite element software ABAQUS as a supplement of the experimental studies.