Abstract: Aiming at the problem that most of the image encryption algorithms are low security and can't resist the choice of plaintext attack, an image block encryption algorithm based on Lorenz mapping and Logistic mapping is proposed. The algorithm first uses Logistic mapping to scramble the plain image. Secondly, the image after the scramble are divided into blocks. Then, the chaotic sequence generated by the Lorenz map is used to perform the intra-block diffusion operation and the inter-block diffusion operation respectively, and the encrypted cipher image is finally obtained. Experimental results show that: the algorithm has large key space, high sensitivity and good encryption effect.