Aiming at the problem of image tampering and forensic localization,a fragile watermarking algorithm based on chaos sequence and image QR decomposition was proposed to determine the image tampering.The algorithm chooses QR decomposition to decompose the image,embeds the watermark after the image is decomposed,and encrypts the watermark by chaotic system to enhance the security of the watermark.Experimental results show that the algorithm not only improves the security of the location watermarking algorithm,but also can estimate the tampering strength of the tampered area.