Abstract: A helmet structure includes a cap body and a setoff element. A plurality of slots is distributed on an interior surface of the cap body. A rubber strip fills each of the slots. The protruding ribs are distributed on an external surface of the setoff element in a manner to match respectively with the slots of the cap body. Since the soft rubber has a high frictional contact, the U-shaped rubber strips not only fit the slots but also tightly attaches to the protruding ribs. Therefore, the cap body is firmly attached the setoff element. However, when the helmet is to be cleaned; the setoff element and the cap body are easily dismounted by pulling the protruding ribs out of the slots without the need of any tool.