The present disclosure relates to a display module, a display device, and an assembling method of the display module. The display module includes: a display panel; a backplane disposed on one side of the display panel away from a light emitting surface of the display panel; a reflective sheet disposed between the display panel and the backplane; and an adapter bracket disposed between the reflective sheet and the backplane, and configured to connect with an external support structure located outside the display module, wherein the adapter bracket has a first surface and a second surface, the first surface is fixed on a surface of the backplane adjacent to the display panel in a surface contact manner, and the second surface supports the reflective sheet.