Most image encryption algorithms are applied to the whole image,so the efficiency of encryption,decryption and transmission is low.According to the characteristics of local image,the image is divided by adaptive block method and a variety of block classification techniques.With the chaotic sequence by Logistic mapping,the de-composed image sequences are encrypted respectively with different encryption keys.The experiments prove that this method increases the periodicity and security of output key sequence.It also improves the speed of encryption,decryption and transmission.The results of encryption and decryption are good.