The invention discloses a part capable of absorbing moisture in a small micro space and continuously and rapidly heating to discharge the moisture in one way and a preparation method and an automobilelamp back cover. Expanded polytetrafluoroethylene coating films are connected to the end surfaces of the two sides of a cylinder body; a reversible moisture absorption particulate matter is filled inthe cylinder body; at least one electric heating element is arranged in the reversible moisture absorption particulate matter; a die cutting product of the expanded polytetrafluoroethylene coating film is welded with the end surface of one side of the cylinder body; the electric heating element is assembled in the cylinder body; the reversible moisture absorption particulate matter is filled intothe cylinder body again; a die cutting product of the expanded polytetrafluoroethylene coating film is welded with the end surface of the other side of the cylinder body; the automobile lamp back cover comprises the part; and the part is assembled in a back cover shell with a plurality of through holes. Through adoption of the mode, the part capable of absorbing the moisture in the small micro space and continuously and rapidly heating to discharge the moisture in one way has the advantages that no fogging and condensation phenomenon in the shell of the small micro space can be guaranteed, the electrical performance in the shell cannot be affected by the humid air environment, and the mist liquid phenomenon cannot be caused on the mirror face or the surface of a smooth electronic elementin the small micro space shell.