The large-diameter pile-enhanced gravity-type anchorage has high anti-sliding capability through lateral load-resistance of the large-diameter piles, and thus has decreased volume and self-weight. As a result, the amount of excavation can be reduced and disturbance to the original ground can be reduced to a minimum. In addition, the piles can help resist the movement of the anchorage under geohazards. However, the combined anti-sliding mechanisms of the rock-socketed piles with the friction between anchorage foundation and ground are unclear, and a practical design method is desired. In this paper, the three-dimensional elasto-plastic finite element method is employed to study the lateral load-carrying capacity of pile-enhanced gravity-type anchorage. To do so, lateral resistance of rock-socketed piles with four different lengths is examined first, and then the coupled anti-sliding capacity of the pile with the foundation friction is investigated for the single-pile-enhanced and the pile-group enhanced anchorage on mediumly weathered sandstone. The cap plasticity model in geomechanics considering volumetric yield of high porosity rocks and the Coulomb contact-friction elements are used in the analysis. The reaction of the rock along the pile depth and the friction between the anchorage and the subsurface are analyzed. The influence of the pile length and layouts on load-carrying capability of the anchorage is examined. It is shown that the piles can take up approximately 70%-80% of the total anti-sliding force, while the actual mobilized friction reaches only 2/3 of the control value. The anti-sliding stability factor of the anchorage is able to meet the requirement of the design code. With well-designed piles, the maximum horizontal displacement of the anchorage can be controlled within 1/10 000 of the main span length. The failure of the pile-enhanced anchorage is caused by the yielding and collapse of the rock around the base-expanded piles on the rear of the anchorage. Compared to the stepped-bottom gravity anchorage, the pile-enhanced gravity anchorage could reduce the self-weight by more than 20%, and is beneficial for green construction of long-span suspension bridges.