The present disclosure provides a thin film transistor, a manufacturing method of the thin film transistor and a display device, configured to improve electrical property of the thin film transistor. The thin film transistor includes: an active layer, including a source and drain contact region and a channel region; a metal barrier layer, covering the source and drain contact region; a first gate insulating layer, at least covering the channel region and exposing the metal barrier layer; a gate, on the first gate insulating layer and covering the channel region; an inner layer dielectric layer, on the gate and having a through hole exposing the metal barrier layer; and a source and drain, on the inner layer dielectric layer and in contact with the metal barrier layer through the through hole.