Abstract: The whole encryption algorithm includes two steps.Firstly,scramble the original image before the DCT transformation block by block with the size8×8;it makes the image disorderly and unsystematic.Secondly,after the quantization of the DCT coefficients,we recompose the double 8×8 DCT blocks border upon,put low coefficients into one 8×8block and put the high coefficients into another one.Shuffle the low coefficients block and high coefficients block with different ergodic matrixes.This algorithm could change the frequent structure while increase the compressed image data a little and change the number of the nonzero DCT coefficients so as to defend the nonzero-counting attack.