Abstract: A chaotic encryption algorithm is presented based on the storage characteristic of color images. Firstly,Lorenz chaotic sequences are preprocessed.Then the sequences are used to build scrambling index matrices.Finally,tricolor scrambling transformation is realized in space domain.Experimental results show that the proposed algorithm has better scrambling effect in comparison with Arnold transformation.The algorithm’s encryption efficiency is very high thanks to the exploitation of all the three outputs of the system and the scrambling of 8×8 units in spatial domain.Since the secret-key space is much larger that the lowdimensional chaotic systems,the proposed algorithm has very good secrecy and security performance.