Relying on the Nayong bank gravity anchorage project of Zangkejiang River Super Large Bridge, the method of combining three-dimensional numerical simulation of FLAC^3D with theoretical analysis were adopted, the mechanical response of the gravity anchorage-foundation system under overload conditions were simulated, the displacement of the anchorage, the shear bearing characteristics of the rock mass clamped by the tooth sill and the evolution law of the plastic zone, as well as the stability of the system were analyzed, and the combined bearing mechanism of gravity anchor structure and foundation. The results show that the ultimate bearing capacity of Nayong bank gravity type anchorage is 6P. The anchorage is displaced under the action of the cable force load, and then the common bearing of the surrounding foundation rock mass is mobilized through the friction of the base and the clamping effect of the tooth sill. The order of the bearing of the rock mass mobilized is to mobilize each tooth sill step by step from the base, and the rock mass clamped by the tooth sill provides passive resistance through shear resistance. The theoretical analysis and numerical simulation results all show that the stability coefficient of the gravity anchorage-foundation system can reach more than 6.0 when the friction and the clamping effect of the tooth sill are considered simultaneously, which is much larger than the stability coefficient when the friction effect is considered only.