In this paper, it is pointed out that the block cipher proposed in “Design of Block Cipher substitution network on chaos” can be broken by attack with known plaintext and attack with ciphertext only, and the key of this cipher can be found by the divide-and-conquer attack with the encipher transformation. Furthermore, the mutual restriction between the successive values of the chaos sequences based on the Logistic mapping, and the property that the frontal values of the chaos sequences are not sensitive to the bits on the lower po-sitions of the initial value are also pointed out.