The invention discloses an array substrate preparation method, an array substrate, and an organic light-emitting display device. The preparation method comprises the following steps: (1) sequentially forming a first metal layer, a first insulating material layer and a second metal layer, which cover a thin-film transistor region and a capacitor device region, on a substrate; and (2) etching the second metal layer, the first insulating material layer and the first metal layer with photoresist and a half-tone mask on the second metal layer, forming a source and a drain which are separated, a gate insulating layer and a bottom gate in the thin-film transistor region, and forming a second electrode, a first dielectric layer and a first electrode in the capacitor device region. Thus, the source, the drain, the gate insulating layer and the bottom gate of the thin-film transistor can be etched by one half-tone mask, the second electrode, the first dielectric layer and the first electrode of the capacitor device are formed at the same time, and the process is simplified. The array substrate of the invention has a dual-gate thin-film transistor and a capacitor device connected in parallel with two capacitors. The capacitor capacity is improved on the basis of increasing the driving force.