Embodiments of the present invention relate to a thin-film transistor (TFT) and a manufacturing method thereof, an array substrate and a manufacturing method thereof, and a display device. The TFT includes an active layer, an amorphous silicon (a-Si) connecting layer and a source-drain electrode layer. The active layer includes a channel region, a source region and a drain region; forming materials of the channel region include polycrystalline silicon (poly-Si); the a-Si connecting layer is disposed on a side of the active layer and includes a first connecting part and a second connecting part which are spaced from each other; the source-drain electrode layer includes a source electrode and a drain electrode which are spaced to each other; the source electrode is electrically connected with the source region through the first connecting part; and the drain electrode is electrically connected with the drain electrode through the second connecting part.