As a main method for copyright protection,the technique of watermarking has been widely studied and applied.A digital watermarking based on Arnold chaotic mapping is proposed.The original watermarking is permuted by using Arnold chaotic mapping.M-sequence is used to spread the watermark signal in order to improve its robustness spectrum,and then the permuted watermarking signal is embedded into wavelet transform coefficients of host image.The experiment results show this algorithm has very excellent effect.