Abstract: In order to protect digital image′s information, an image encryption algorithm based on Lorenz chaos sequence and similar CBC (Cipher Block Chaining) mode is presented． Firstly, 3D Lorenz chaotic sequences are improved to be with ideal pseudo-randomness. Then, the image′s pixel positions are shifted by using the 3D sequence. The image is divided into blocks, and the pixel value in each block is altered based on the 3D sequence and CBC, so that the image will be scrambled and encrypted. While doing the decryption, a method is provided based on the neighboring pixels characteristic to renew the image attacked by shearing. Lastly, the effects of encryption, decryption and security are also analyzed by using the method of accessing.