A thin film transistor includes: a bottom gate electrode; a bottom gate electrode insulating layer, a semiconducting active layer and a first insulating layer which are disposed on the bottom gate electrode in sequence; a source electrode and a drain electrode which are disposed at a side of the first insulating layer away from the bottom gate electrode; vias disposed in the first insulating layer at positions which correspond to the source electrode and the drain electrode respectively; and ohmic contact layers disposed on and covering the semiconducting active layer at positions corresponding to the vias respectively. Each of the source electrode and the drain electrode is in contact with a corresponding one of the ohmic contact layers through a corresponding one of the vias.