The invention discloses a preparation method of a gamma-TiAl-based alloy bar. The preparation method comprises the following steps: (I) preparing a gamma-TiAl alloy ingot through a vacuum melting method; (II) manufacturing a jacket, wherein the jacket comprises a jacket cylinder and jacket covers, the jacket covers are used for sealing the two end openings of the jacket cylinder, and each jacket cover is provided with a ventilating hole; (III) thermally treating the cylinder body, subsequently coating the inner wall of the cylinder body with an oxidation-resistant coating, afterwards putting the TiAl alloy ingot in the cylinder body and finally welding each jacket cover on the corresponding open end of the cylinder body; (IV) externally coating the oxidation-resistant coating, carrying out thermal treatment, subsequently extruding in an extruder to obtain the bar, and straightening the bar by letting the bar directly pass through a straightening tube; and (V) removing the jacket on the outer surface and carrying out homogenizing annealing treatment to obtain the gamma-TiAl-based alloy bar. The problem that a TiAl intermetallic compound is relatively large in brittleness and easy to oxidize in a hot working process can be solved through the preparation method disclosed by the invention, and the prepared gamma-TiAl-based alloy bar is uniform in microstructure and high in mechanical property.