A method of manufacturing a thin film transistor is provided, and includes: providing a substrate; depositing a buffer layer and patterning the buffer layer; sequentially depositing an insulation layer and a first metal layer, coating a photoresist on the first metal layer; metal etching the first metal layer; ashing the photoresist; metal etching the first metal layer of the lightly doped region; implanting ions to an active area; and removing the photoresist.