The utility model discloses a high-low plate semitrailer with a liftable platform, which comprises a gooseneck type main frame, a fixing platform arranged at the upper part of the front end of the gooseneck type main frame, and a liftable platform arranged at the upper part of the rear end of the gooseneck type main frame, and the liftable platform has two states; in the first state, the liftable platform is lower than the fixed platform; and in the second state, the liftable platform is flush with the fixed platform. The semitrailer has the advantages that the semitrailer has various forms, can be used as a high-low plate semitrailer and can also be used as a flat plate semitrailer; and compared with a common high-low plate semi-trailer or a flat plate semi-trailer, the transported media are more diversified.