Abstract: A new chaotic encryption algorithm based on combining Logistic map and Mix Optical Bistability（MOB） model is proposed.The chaotic sequences of the Logistic maps and MOB are adopted to generate key sequences for the image encryption，respectively.The cryptosystem is further made robust against any reasonable attack by using the feedback technique.Simulation results show that the proposed cryptosystem requires very little time to encrypt the plaintext.The key space is large enough to resist the brute-force attack.The chiptext varies sensitivly with the variances of the secret key and the plaintext.For the encrypted image the distribution of pixel-values have a radom-like behavior and the values of adjacent pixels satisfy zero correlation，showing that the proposed scheme is of high security.