The image encryption is a very important area of information security. Also encryption is one of the core technologies in information security control. To the network transmission and communication security, encryption has become the most effective way. It puts the higher requirements to the technology of encryption and decryption of information in the modern network information system. Not only does it ensure the security and coherence of information, but also demand the high efficiency. As it refers to the research and selecting of encryption technology, two elements must be included, that is, security and high efficiency. In this paper, an improved scrambling method based on Arnold transform for two-dimensional digital image is proposed. The algorithm has been improved in order to enhance its security and efficiency.