An embodiment of the invention provides a manufacturing method of a thin-film transistor includes: providing a substrate; sequentially forming a gate electrode, a gate insulating layer, and an active layer on the substrate; forming an insulating metal oxide layer covering the active layer, wherein the insulating metal oxide layer including a metal oxide of a first metal; forming a metal layer covering the active layer, wherein the metal layer includes a second metal; forming a source electrode and a drain electrode on the metal layer with a trench separating therebetween; removing the metal layer exposed by the trench; and performing an annealing process to the metal layer and the insulating metal oxide layer, such that the metal layer reacts with the insulating metal oxide layer overlapping the metal layer to form a conducting composite metal oxide layer including the first metal and the second metal.