The invention relates to a key management method for the media flow based on the IP multimedia subsystem, the key acquisition and the distribution control are operated by the application server and stream media sever uniformly, the application server can distribute the TEK to the terminal and the stream media sever, the TEK can be used in the content of encrypted stream media sever and the terminal; the application server can adopt the layered key management method, and it can send the key encrypted key KEK to the terminal and stream media sever, and it can develop the TEK by the KEK. The invention also relates to a key management system for the media flow based on the IP multimedia subsystem. The system and method of key management can make the function of key management more simplified and legible, additionally, the stream media sever can't need to save the key information of terminal, and the key can be obtained interactively between the application sever to reduce the cost of key management of stream media sever, and improve the efficiency of stream media sever.