A method for renewing the rail substructure of a rail track, the rail substructure consisting of a layer of gravel and a layer of substructure located below the layer of gravel, with use being made of two separate work units (1, 2) that can be operated independently of each other and used individually, wherein, in a continuous sequence of operations, the first work unit is used to remove and recondition the old layer of gravel and to install reconditioned and/or new gravel and the second work unit is used to remove the old layer of substructure and to install a reconditioned and/or new layer of substructure, and wherein the work units (1, 2) comprise material conveying wagons (7, 8, 16), characterised in that the two work units (1, 2) can be moved independently of each other and coupled to each other, wherein - for the purpose of renewing the layer of gravel, the first work unit comprises not only an assembly for removing, reconditioning and installing the gravel of the layer of gravel but, additionally, also first material conveying wagons for intermediately bunkering the reusable portion of the gravel and second material conveying wagons for intermediately bunkering the non-reusable portion of the gravel, wherein the second material conveying wagons are arranged directly adjacent to the second work unit, and - for the purpose of renewing the layer of substructure, the second work unit comprises an assembly ahead of the end thereof for removing the old layer of substructure and installing the new layer of substructure and, behind this assembly ahead of the end thereof, a buffer wagon and third material conveying wagons, wherein, in the initial state of a working cycle, the third material conveying wagons are filled with new substructure material, wherein - in a continuous forward motion, the assembly of the first work unit is used to remove and immediately subsequently clean the layer of gravel and to intermediately bunker a fraction of recycled, reusable gravel in the first material conveying wagon and the non-reusable waste gravel in the second material conveying wagon, - the second work unit including the assembly ahead of the end thereof is used to remove the old layer of substructure and immediately install the new material which is stored in the third material conveying wagons, wherein the removed old substructure material is supplied to fourth material conveying wagons which, at the beginning of the working cycle, are represented by the buffer wagon and subsequently by emptied third material conveying wagons, - the second material conveying wagons are decoupled from the first work unit and coupled to the second work unit as soon as the second material conveying wagons are filled with the old gravel and the third material conveying wagons are filled with the old substructure material and the new unit thus formed is moved to a storage place opposite to the working direction, where the materials from the material conveying wagons (8, 16) are intermediately stored separately from each other and the third material conveying wagons are filled with new substructure material, and - the first work unit applies the recycled gravel onto the new layer of substructure in the meantime. - for the purpose of renewing the layer of gravel, the first work unit comprises not only an assembly for removing, reconditioning and installing the gravel of the layer of gravel but, additionally, also first material conveying wagons for intermediately bunkering the reusable portion of the gravel and second material conveying wagons for intermediately bunkering the non-reusable portion of the gravel, wherein the second material conveying wagons are arranged directly adjacent to the second work unit, and - for the purpose of renewing the layer of substructure, the second work unit comprises an assembly ahead of the end thereof for removing the old layer of substructure and installing the new layer of substructure and, behind this assembly ahead of the end thereof, a buffer wagon and third material conveying wagons, - in a continuous forward motion, the assembly of the first work unit is used to remove and immediately subsequently clean the layer of gravel and to intermediately bunker a fraction of recycled, reusable gravel in the first material conveying wagon and the non-reusable waste gravel in the second material conveying wagon, - the second work unit including the assembly ahead of the end thereof is used to remove the old layer of substructure and immediately install the new material which is stored in the third material conveying wagons, wherein the removed old substructure material is supplied to fourth material conveying wagons which, at the beginning of the working cycle, are represented by the buffer wagon and subsequently by emptied third material conveying wagons, - the second material conveying wagons are decoupled from the first work unit and coupled to the second work unit as soon as the second material conveying wagons are filled with the old gravel and the third material conveying wagons are filled with the old substructure material and the new unit thus formed is moved to a storage place opposite to the working direction, where the materials from the material conveying wagons (8, 16) are intermediately stored separately from each other and the third material conveying wagons are filled with new substructure material, and - the first work unit applies the recycled gravel onto the new layer of substructure in the meantime.