An optimized watermark algorithm based on discrete wavelet transform (DWT) was put forward, which can resist to printing and scanning. The algorithm divides wavelet coefficients into low frequency, middle frequency, and high frequency. Watermark of different intensities was applied to guarantee invisibility and increases robustness according to different resolutions of human vision to the three coefficients. Pretreatment process was added while extracting scan image to enhance the extraction accuracy watermark information. Experiments showed that the algorithm has good robustness to shear, noise, compression attacks.