We propose the use of a method to encrypt the colour image with scrambling diffusion which combines the traditional cat mapping and the chaotic sequence,the method overcomes the defects of cat mapping in periodicity and being vulnerable to chosen-plaintext attack.The algorithm uses the Logistic mapping and the Chebychev mapping.First,it uses the equilibrium of Chebychev mapping to generate the key which controls the parameter of Logistic mapping,and generates a variety of Logistic sequence with different parameters,then it uses the Logistic sequence to control the range of image scrambling,and employs Lorenz system to get the key and the scrambling times of every Arnold transform.When the scrambling is completed,the algorithm uses Lorenz system again to control the operation variables which are used in diffusion.Experimental simulations indicate that the algorithm has better scrambling diffusion effect on the image,and overcomes the shortcoming of cat mapping,it brings large key space,and can encrypt the image with high quality as well as resist common attacks.%提出一种使用传统的 Cat 映射与混沌序列结合的方法对彩色图像进行置乱扩散加密，克服了 Cat 映射周期性与易受选择明文攻击的缺陷。算法使用了 Logistic 映射和 Chebychev 映射。首先利用 Chebychev 映射的平衡性产生密钥，控制 Logistic 映射的参数，产生多个不同参数的 Logistic 序列；再用 Logistic 序列控制图像置乱的范围，使用 Lorenz 系统得到每次 Arnold 变换的密钥和置乱次数。置乱完成后，再使用 Lorenz 系统控制扩散时操作的变量。实验仿真表明：该算法对图像有比较好的置乱扩散效果，克服了Cat 映射缺点，并且具有很大的密钥空间，能够高质量加密图像并抵抗常见的攻击。
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