The utility model relates to the technical field of external expansion cups, in particular to a stable gathering external expansion cup, which comprises a central position, a left cup and a right cup, the left cup, the central position and the right cup are integrally connected without steel rings, and each of the left cup and the right cup comprises a cup outer layer, a cup middle second layer, a cup middle first layer and a cup inner layer. According to the utility model, the gathering effect, the stability and the comfort of the traditional bra are improved through the design of steel-ring-free integral forming, a multi-layer cavity structure, elastic body filling, flank-free and underband-free, the steel-ring-free design provides soft support and reduces the oppression of ribs and breasts, and the combination of the multi-layer cavity structure and the elastic body improves the comfort of the bra. The chest gathers stably, fat is prevented from expanding outwards, wearing portability and comfort are improved due to the design without side wings and undercuts, the gathering effect is further enhanced through the inner-layer protruding positions, the chest shape is modified, and the chest is plump, tall and straight.