Methods for fabricating an IGZO layer and fabricating TFT are provided in the present invention. The method for fabricating TFT includes the following steps: (1) depositing an IGZO layer and forming a surface oxidizing gas protective layer on the IGZO layer; (2) coating the IGZO layer with a photoresist, and then subjecting the photoresist to an exposing and developing process to form a photoresist pattern; and (3) subjecting the IGZO layer to an etching process, and then removing the photoresist. By forming an oxidizing gas protective layer, the present methods for fabricating an IGZO layer and fabricating TFT can effectively reduce the effect of hydrogen atom on IGZO layer and avoid the change of IGZO layer from semiconductor to conductor, thereby improving the stability of the IGZO layer and thus the TFT, and reducing the negative bias of threshold voltage generated by the long-term continuous use of the device.