The present invention belongs to the field of display technology and provides a thin film transistor and a manufacturing method thereof, an array substrate and a display device. The thin film transistor comprises a gate, a source, a drain and a plurality of insulating layers, wherein at least one insulating layer comprises a Group VB metal oxide. Since the insulting layer is formed by using the Group VB metal oxide which has high dielectric constant, the thickness of the insulating layer can be reduced and the thin film transistor can be miniaturized.