The present disclosure provides a method for producing a thin film transistor. The method includes the steps of: forming a protective layer on an active layer of the thin film transistor and patterning the protective layer along with the active layer when the active layer is deposited; depositing a source and drain electrode layer and patterning it by a dry etching to form a source electrode and a drain electrode; and etching or passivating the protective layer located in a back channel region of the source electrode and the drain electrode. In addition, the present disclosure also discloses a thin film transistor produced by the above method, and an array substrate.