An embodiment of the present invention provides a fabricating method of a thin film transistor, a fabricating method of an array substrate, and a display device. The fabricating method of a thin film transistor comprises: forming a gate electrode on a substrate; and forming a gate insulating layer, a semiconductor layer, source and drain electrodes and a channel region on the substrate, wherein, the semiconductor layer is formed of a metal oxide, and two etching steps are used to form the channel region, and in a first etching step, a part of a source-drain metal layer above the semiconductor layer corresponding to the channel region is removed by using a dry etching, and in a second etching step, a remaining part of the source-drain metal layer above the semiconductor layer corresponding to the channel region is removed by using a wet etching, thereby forming the channel region.