The present invention relates to a method for manufacturing a thin film transistor and an array substrate, and corresponding devices. In the thin film transistor manufacturing process, the base substrate is annealed after the formation of the patterns of the active layer, the source and the drain in the thin film transistor, so as to thermally diffuse ions of the source and the drain at an ohmic contact between the active layer and the source, as well as the drain, to the active layer, and further to provide the active layer with ions of the source and the drain for changing the components of the active layer, which reduces the resistance at the ohmic contact between the active layer and the source, as well as the drain, and guarantees the uniformity and reliability of the thin film transistor. Moreover, annealing treatment is relatively simpler in implementation as compared with the plasma treatment, and will not increase the complexity of the method for manufacturing the entire thin film transistor, which is good for thin film transistor production efficiency.