Abstract: This paper proposes an image encryption method based on spatiotemporal chaos.Firstly，the balance of the pseudorandom sequences produced by two way coupled map lattice model is researched and improved.Then，the image key and the external key，which can resist an exhaustive attack and a known-plaintext attack，are proposed.Finally，the whole encryption process is realized by the confusion of the image pixels’ values and the permutation of the pixels’ positions.The security analysis shows that the method has very good encryption effect.