The invention discloses a thin-film transistor, a preparation method thereof, an array substrate and a display device The thin-film transistor comprises a substrate, and a gate electrode, a gate insulation layer, an active layer and a source and drain electrode layer which are arranged on the substrate, wherein the source and drain electrode layer comprises a source electrode and a drain electrode; and the thin-film transistor also comprises a light blocking layer arranged around the active layer. The light blocking layer is arranged around the active layer, and the side surface of the active layer can be prevented from being affected by light irradiation, so that leakage current of the thin-film transistor caused by a photon-generated carrier generated by the light irradiation active layer is reduced.