The invention provides a thin film transistor, an array substrate and a display device. The thin film transistor comprises a conductive oxygen vacancy reducing layer for reducing oxygen vacancies in an active layer. The oxygen vacancy reducing layer is disposed between the active layer and a source and/or the active layer and a drain. With the oxygen vacancy reducing layer, the number of the oxygen vacancies in the active layer is decreased greatly, which improves transmission rate of carriers and simultaneously reduces value of subthreshold swing of the thin film transistor.