Network storage provide high scalability, availability and flexible for storage systems, and are widely applied to many fields. Small I/O seriously affects the performance of the storage system including network storage. Current several met hods want a theory model and only improve write performance. In this paper, the aggregate I/O model is presented first. Moreover, how to apply this methodology in a NAS system is also illustrated based on IP network. The aggregate I/O modul e called CFS (chunk file system) is designed at both the NAS device and the cust omer end. In the experiment, the analysis of the results shows correctness of th e model and an improvement made by aggregate I/O for network storage performance .