In this paper,a chaotic modulation digital image zero-watermarking method is proposed.Select some low frequency wavelet coefficients of original or tested image and compute the character of the selected coefficients to create watermarking.The wavelet coefficients is randomly selected by the chaotic method.The experimental results show that the watermarking method is invisible and robust against some image processing such as median filtering,JPEG compression,additive Gaussian noise,cropping and rotation attacks and so on.This method changes the traditional doings that watermarking is embedded into images,and make the watermarked image distortion-free.If the initial value of chaos is unknown,the characteristic watermarking can not be extracted correctly.