The present application discloses a fabricating method for a thin film transistor, including steps of: S1, filling filling materials into the pores of the porous substrate to obtain a carrier substrate; S2, fabricating a flexible film layer on the carrier substrate; S3, removing the filler material; S4, fabricating an organic light emitting diode on the flexible film layer; and S5, removing the porous substrate to obtain the thin film transistor. The fabricating method of the thin film transistor according to the present application is based on a porous substrate having a microporous structure, due to the presence of microporous, the bubbles generated during the OLED fabricating process can be released to avoid the damage of the bubbles during the laser irradiation and to the deposition metal mask; and eliminating the process of removing the sacrificial layer by laser irradiation, and the heating the heating process in the conventional technology.