Abstract: An overall instability occurred in a makeshift aluminum alloy truss roof． Through site reconnaissance and combined with the design drawings，the property of the aluminum alloy material and the structure bearing capacity were analyzed． The mechanical properties of aluminum alloy differ from those of steel． Based on the current basic methods for design of aluminum alloy structures at home and abroad，in light of the main，secondary causes of this accident，the aluminum alloy welding and the adverse influence on the structure under wind load were analyzed．