Abstract: Based on the compound chaos and affine transformation in finite integer domain,an encryption algorithm is proposed to embed into the compression of JPEG image.Firstly,the blocks of 8×8 pixels of R,G and B components are scrambled globally in space domain to disarrange the combination relation among three components before the precedence of normal JPEG compression.Secondly,the frequency domain’s DC coefficients of brightness and color components are scrambled respectively after quantization,and their values are mixed according to the corresponding coordination.Lastly,the compound chaos system is perturbed to substitute for the DC coefficients self-adaptively.Our algorithm is designed modularly with huge key space and high security.The experiments showed that the algorithm produce results with high visual quality with strong sensitivity,and could generate the ciphertext with almost the same size as that of the directly compressed image.