The present disclosure relates to the field of display technology and provides a method for manufacturing a TFT, the TFT, an array substrate including the TFT, and a display device. The method includes steps of forming a pattern of a gate electrode on 5 a base substrate, forming a gate insulation layer on the base substrate, and forming patterns of a source electrode and a drain electrode arranged above the gate insulation layer. The method further includes forming an antioxidation metal protection layer on a surface or surfaces of the gate electrode, the source electrode and/or the drain electrode.