A thin film transistor and a manufacturing method thereof, an array substrate and a display device are provided. The method includes forming a gate electrode, a gate insulating layer, a metal oxide semiconductor (MOS) active layer, a source electrode and a drain electrode on a substrate. The MOS active layer includes forming a pattern layer of indium oxide series binary metal oxide including a first pattern directly contacting with the source electrode and the drain electrode. An insulating layer formed over the source electrode and the drain electrode acts as a protection layer, the pattern layer of indium oxide series binary metal oxide is implanted with metal doping ions by using an ion implanting process, and is annealed, so that the indium oxide series binary metal oxide of the third pattern is converted into the indium oxide series multiple metal oxide to form the MOS active layer.