The invention discloses a hot straightening method for controlling the shape of an extra-thick plate, and belongs to the technical field of hot straightening machines for medium-thick plates. The method comprises the following steps of: at the last time when a steel plate is rolled, sending steel plate production data by a rolling machine to a straightening machine, and performing straightening precomputation by the straightening machine on the extra-thick plate; supplying corresponding precomputation parameters, wherein setting ranges of the parameters are that: a straightening force ranges from 1,000 to 5,000 KN, and a straightening speed ranges from 0.2 to 0.7 m/s; and when the steel plate reaches the 1# grating of the straightening machine, starting an extra-thick plate straightening mode, namely setting corresponding straightening roller slits according to different thicknesses and temperatures of the steel plate, and setting the roller slits according to two temperature ranges and three thickness ranges. The invention has the advantages that: the method is easy to operate, and is safe; the problem that the rolled steel plate with the thickness of over 100 millimeters cannot be straightened is solved; a technical guarantee is supplied to control over the shape of the extra-thick plate; and straightening equipment can be protected.