Some work is done to improve embedding capacity and locate tampered regions base on the prior research of fragile document watermark in this paper. And an effective fragile document watermarking algorithm is proposed. The wet paper code which adjusts the number of embedding watermark bits dynamically and takes full advantage of turnover pixels is used for embed watermark to improve embedding capacity. To locate tampered regions, the image is cut into blocks according to the content of it and every image block includes only one character or Chinese word. The Gray-code which was used for coding the watermark reduced the decoding errors caused by noise and improved the robustness of the watermark. The experiment shows that this algorithm can detect the location of tampered image and get better embedding capacity that is near the number of changeable pixels, which are demands of actual application.