According to the similarity between the watermarking system and communication system, this paper applies the convolutional encoding and interleaving technques to image digital watermarking algorithm. The watermark is processed by toral automorphism, convolutional encding and interleaving before embedding, in order to improve the security and robustness. According to the watermarking information,the DC coefficients are quantized in order to extract the watermarking information without original image. The experiment shows that the algorithm is robust to salt and pepper noise, gaussian noise,compression,filtering and cropping.