Abstract: In order to deeply research the effects of stay cable breaking,relative interface slip of composite girder and deck shear-lag effect on structural ultimate load-bearing capacity,Guanyinyan composite girder cable-stayed bridge in Jiangjin in Chongqing,as the engineering background,was investigated by considering geometrical nonlinearity,material nonlinearity,system transition and cumulative effect of displacements and stresses and adopting the theory of second kind static stability.The research results show that stay cable breaking,relative interface slip of composite girder and deck shear-lag effect have great influences on safety factor for the ultimate bearing-capacity of a long-span composite girder cable-stayed bridge,and the maximum variation of the safety factor resulted from them are respectively 23.0%,19.0% and 42.4%.The effect of stay cable breaking on the ultimate load-bearing capacity increases firstly and then decreases gradually,while the influences of the relative interface slip and the deck shear-lag effect behave mainly at the stage of short cantilever.