The utility model relates to the technical field of luggage storage accessory devices, in particular to a luggage undercarriage, which is convenient for passengers with short stature or smaller physical strength to take and place luggage and improves the use reliability. The size of the storage space can be adjusted according to the actual size of luggage, the luggage fixing effect can be guaranteed, the occupied space can be reduced, and the practicability is improved; the device comprises a placing plate installed in a carriage, multiple sets of partition plates are arranged on the placing plate at equal intervals, and the multiple sets of partition plates divide the top of the placing plate into multiple sets of storage spaces; the device further comprises a plurality of lifting units.The multiple sets of lifting units are all installed at the bottom end of the containing plate. the multiple sets of lifting units are located under the multiple sets of storage spaces correspondingly, each lifting unit comprises a supporting plate, two sets of threaded pipes, two sets of threaded rods, two sets of telescopic supports, two sets of upper ball bearings and two sets of lower ball bearings, a cavity is formed in the rear end of the interior of each supporting plate, and two sets of chain wheels and chains are arranged in each cavity.