Provided is a thin film transistor. A drain electrode groove and a source electrode groove are formed in an indium-gallium-zinc oxide layer, and etching barrier layers are formed on the groove walls of the drain electrode groove and the source electrode groove, so that when a device works, current of a source electrode and a drain electrode is not influenced by a back channel. Due to the fact that the grooves are formed in the indium-gallium-zinc oxide layer, the thickness from the contact face between the source electrode and the indium-gallium-zinc oxide layer to a gate electrode insulation layer is decreased, the thickness from the contact face between the drain electrode and the indium-gallium-zinc oxide layer to the gate electrode insulation layer is decreased, and accordingly series resistances of the source electrode and the drain electrode are reduced. The invention further discloses a manufacturing method of the thin film transistor.