The present disclosure provides a manufacturing method of a thin film transistor, including: selecting a substrate, and forming a bottom gate, a gate insulating layer and a source-drain above the selected substrate, wherein the bottom gate and the source-drain adopts a conductive metal oxide with an adjustable work function as a metal conducting electrode; rinsing and drying the source-drain of the selected substrate, and ozone cleaning dried source-drain for a predetermined time under a predetermined illumination condition, bombarding the source-drain with oxygen plasma for a period of time, forming an active layer made of a carbon material over the source-drain; forming a passivation layer over the active layer. The implementation of the disclosure can reduce the contact resistance and improve the performance of the carbon-based thin film transistor device by adjusting the work function of the contact surface between the conductive metal and the active layer.