The invention belongs to the technical field of transfer cases, and relates to a high-low-gear switching device, a transfer case and a vehicle. The high-low-gear switching device comprises a planetary gear mechanism and a fixing frame. The planetary gear mechanism comprises a gear sun wheel capable of being fixedly arranged on an input shaft, a gear planetary wheel, a gear tooth ring and a gear tooth sleeve, wherein the gear planetary wheel, the gear tooth ring and the gear tooth sleeve are sequentially arranged outwards in the radial direction; the gear planetary wheel is provided with a gear planetary frame used for outputting power; the gear tooth sleeve can move axially so as to be connected with the fixing frame, so that the gear tooth ring is locked for low-gear power output, or the gear tooth sleeve can move axially so as to be connected with the gear planetary frame, so that the gear tooth ring and the gear planetary frame are fixedly connected for high-gear power output, thus, the gear tooth sleeve of the planetary gear mechanism can be combined with different parts, and high-low-gear switching in the vehicle advancing process is achieved.