The invention relates to the technical field of semitrailers, in particular to a retractable frame for a low flat-bed semitrailer. The retractable frame structurally comprises a fixed frame assembly, a movable frame assembly, a rolling wheel device and a locking device which is used for fixing the movable frame assembly in the horizontal direction; the rolling wheel device is arranged on the fixed frame assembly and/or the movable frame assembly, and is used for supporting the fixed frame assembly, and enabling the movable frame assembly to move in a retractable manner in the horizontal direction relative to the fixed frame assembly. Compared with the prior art, the retractable frame provided by the invention has the advantages that retractable length adjustment of the whole frame is realized; when a larger carrying capacity is required to be met, the whole frame can be lengthened; during routine use, the whole frame can be shortened to avoid various inconvenience caused by the relatively long frame body during use, so that different carrying capacity requirements can be met; the operation is simple, the use is convenient, and the production cost of the frame is reduced.