The invention discloses a battery case film covering method. The method includes the steps that firstly, a thin film is led out of a thin film roll and conveyed through a thin film conveying roller set, passes a pair of lifting thin film rollers and is finally clamped through a thin film clamping device; then, a battery case is conveyed along a battery case conveying mechanism, after a position sensor detects that the battery case is conveyed to the tail end of a battery case conveying belt, a battery case grabbing structure grabs the battery case on the battery case conveying belt, the battery case grabbing structure is then driven by a sliding board to move backwards, when the battery case is located above a battery case film covering platform, the battery case is placed on the battery case film covering platform through the battery case grabbing structure, and at the moment, the bottom face of the battery case is already covered with the thin film; then, after the pair of lifting thin film rollers ascend, the sliding board drives a thin film conveying mechanism to move forwards, the upper surface of the battery case is covered with the thin film, and the whole battery case is covered with the thin film; and finally, a thin film cut-off mechanism acts to finish a work circulation. By the adoption of the method, actions of equipment are fewer and work is reliable.