A manufacturing method of an active layer of a thin film transistor is provided. The method includes following steps. First a substrate is provided, and a semiconductor precursor solution is then prepared through a liquid process. Thereafter, the semiconductor precursor solution is provided on the substrate to form a semiconductor precursor thin film. After that, a light source is used to irradiate the semiconductor precursor thin film to remove residual solvent and allow the semiconductor precursor thin film to produce semiconductor property, so as to form a semiconductor active layer.