A three-layer-core single-mode large-mode-area fiber with low bending loss is investigated in this paper. The three-layer structure in the core which is comprised of core-index layer, cladding-index layer and depression-index layer, can achieve large-effective-area Aeff while maintaining low-bending-loss without deteriorating cutoff behaviors. The large-mode-area of 100–330 μm² can be achieved in the fiber. The effective area Aeff can be further enlarged by adjusting the layer parameters. Furthermore, the bending property can be improved in this three-layer-core structure. The bending loss can decrease by 2–4 orders of magnitude compared with the bending loss of the conventional step-index fiber with the same Aeff. These characteristics of three-layer-core fiber suggest that it can be used in large-mode-area wide-bandwidth high-capacity transmission, or high-power optical fiber laser and amplifier in the optical communications, which can be conducive to studying the basic physical layer structure of big data storage, reading, calculation and transmission applications and so on.