The invention relates to a forming die for forming an automobile back door plate. The forming die comprises an upper die body and a lower die body. A power mechanism drives the upper die body to move vertically, and the forming face of the upper die body is far away from or close to the forming face of the lower die body. Blank holders are arranged on the periphery of the forming face of the lower die body. A movable core die body is arranged on the forming face of the lower die body and connected with a lifting mechanism. The lifting mechanism drives the movable core die body to move vertically. The movable core die body is provided with a forming face used for forming a back door plate modeling area. The movable core die body arranged on the lower die body is utilized for being matched with the upper die body, a plate to be formed is placed on the lower die body, the upper die body moves downwards, the upper die body makes contact with the blank holders, and accordingly the plate is pressed. The lifting mechanism can drive the movable core die body to move upwards, the upper forming face of the movable core die body is higher than the forming face of the lower die body, and accordingly the complex modeling area on the back door plate can be formed. The upper die body continues to move downwards to the bottom dead center, and therefore other areas of the back door plate can be formed.