Digital watermarking is a kind of technology of hiding technology which is used to protect the copyright of digital products. In this paper, a new fragile digital watermarking algorithm based on hybrid visual bistable system is proposed. It divides the image into non-overlapped blocks, calculates the luminance of each block to decide the embedding depth and the length of chaotic sequence. For each pixel, an initial value is determined based on its prominent chrominance value, the position index, and the image protection key. Watermarking sequence is embedded into the embedding space of R,G,B respectively. Then it detects the temper by comparing the extracted watermarking and the produced one, until the error image is attained. Theoretical analysis and experiment result show that this algorithm is in high quality and locates the tamper position exactly.