This paper proposes a new type of multi-user digital watermarking based on CDMA, which aims at the demand of multi-user copyright sharing protection. It presents two CDMA based approaches, i.e. wavelet domain direct approach (WD) and wavelet domain neighbor linear prediction approach (WNLP). It analyses the influence of user quantity and embedding depth on the quality of watermarked images and extracted watermarks. Experiment results show that the algorithm can solve the problem of watermarks collision and relieve the restriction of user quantity of multiple watermarking algorithms.