This treatise proposes a new algorithm of encrypting images by combining Sine map with generalized Arnold transformation. The algorithm adds a shift transformation link to the common permutation-diffusion structure. Firstly, the plain-image is permutated in pixel positions by using the generalized Arnold transformation. Secondly, the permutated image is diffused by using the Sine map. Then, the diffused image is performed through the shifting process, which can avoid multiple encryption and shorten the encryption time. The results of analysis and experimental tests for the proposed algorithm have been given in detail, which showed that our new algorithm is highly secure. In conclusion, it has great application potential in Internet-based image secure communication.