Abstract: A colour image cipher based on ergodic matrix and chaos is proposed.Firstly，the red，green and blue channels of the input image are permuted independently by using the ergodic matrixes，which are generated by discrete chaotic maps.Then two rounds of diffusion and encryption operation with the 3D chaotic sequences are adopted to realize the tricolor substitution pixel by pixel.The security of the proposed image encryption technique has been analyzed using various statistical analysis，key sensitivity analysis，differential analysis，key space analysis.The results demonstrate that the algorithm has good properties of confusion，diffusion and statistic distribution of pixel value.The key space is large enough to resist the brute-force attack，showing that the proposed scheme is of good practicability.