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.