With the development of the AMI system, the security of its communication data is of high importance. IEC62056 standard establishes a concrete plan for data encryption, to ensure the confidentiality and integrity of the communication data, but it is lack of the complete key management mechanism, especially in terms of the key control. Based on the security part in IEC62056 standard, we do research on the key management of AMI system, designing a scheme of the key management which is suitable for the AMI system, effectively enlarging the security mechanism of the AMI system, also improving the safety and reliability of the system.