The utility model provides a foldable door. An appropriate gap is left between the ground and the door when the door is opened; however when the door is closed, the gap between the lower edge of the door and the ground is automatically sealed. A plurality of retractile X-shaped flanges are arranged vertically on the foldable door; the X-shaped flanges are connected with each other by wire rods which pass through the pivoting connection points of the X-shaped flanges; surface materials are arranged ahead and behind the X-shaped flanges; sliding components which can slide up and down are arranged at the lower part of the wire rods; motion connection rods are arranged between the wire rods and the sliding components, so that the sliding components descend in the position where the X-shaped flanges are expanded and ascend in the position where the X-shaped flanges are shrunk; and moreover, shielding materials are installed on the sliding components; and the shielding materials are located in position where the sliding components descend for shielding space between the lower edge of the surface material and the ground.