Abstract: Because files in P2P file system have too many copies and those copies are saved in a large-scale network, and the network's delay is very large, so many P2P file systems haven't writing mechanism. Some P2P file systems, like Pond and Ivy, have writing mechanism, but their performance is not good. Digital organism file system is a new file system. It has implemented an efficient writing mechanism. In this writing mechanism, the definition of updating group is given. The idea of updating agent based on updating group is proposed. Streaming updating mechanism, which includes an algorithm to avoid write chaos and an algorithm to control parallel degree and checks the writing error, is proposed. This writing mechanism introduces core update copy set to rule out the copies with low updating speed. The select algorithm for core update copy set is given in this paper. As shown in many tests, updating agent based on updating group idea is helpful for reducing the network spending. In the writing process, good core update copy set will come into being. In the network with large delay, the writing speed of streaming updating is higher than that of synchronous updating. Testing results show that the performance of DOFS is better than that of similar systems.