Stability evaluation of the high and steep slope formed by foundation excavation of a gravity anchorage is a key problem in safe construction and operation of the suspension bridge. Taking the gravity anchorage slope of Taoyuan Jinsha River Suspension Bridge of Dayong Expressway in Yunnan Province as a case study, through the field investigation and geological borehole data, a three dimensional finite element model was established to evaluate the stability of the anchorage foundation slope under the excavation and earthquake actions. The reinforcement effect of the support system including the anti-slide piles, bolts, pre-stressed anchor cable and lattice beam was studied. Using the support system, the maximum displacement of the slope decreased by 41%, and development of the plastic zone of the slope was controlled during the earthquake. The research results are used in the construction and design of this project, and also can be used for reference by the similar projects.