Abstract: In this paper, We used characteristic of the Unified Modeling Language (UML) use case model in describing the function of the system's and the iteration sequence of agile development process to obtain a new iteration sequence based on the risk an value of the various use cases in UML use case diagrams.An obvious advantage of doing so is to ensure high-risk and high-value use cases will be first developed, so that the use cases will be repeatedly tested in the next iteration, thereby increasing overall system reliability.