Study of Fractal in building up the Digital Watermark’s Robusting (1.School of Science, Lanzhou University of Technology, Lanzhou 730050 China ,2. School of Computer and Commucation ,LanZhou University of Technology ,LanZhou ,china, 730050) Abstract: Based on the strongly robusting character against geometric distortion of self-similar fractal and the character of Human Visual System(HVS),a new algorithm for digital watermark is put forward。The method operates in the frequency domain and spatial domain. The digital watermark information is transformed into coefficients of an IFS after the original image has been done frequency transformation, and then the self-similar fractal image created by this IFS is embedded into the special area of the image. The algorithm is tested in robusting against geometric distortion and of imperceptibility of human eyes. Keywords: iterated function system; human visual system; visual masking; digital watermarking