Abstract: We introduced a methodology that starts with the analysis of the UML use case diagram for software reliability allocation with the probability of executing each use cases. We will utilize the probability of executing each use cases to measure the importance of the use case, then to determine weight factor of each use case. According to the weight factor of each use case to determine the reliability index undertaken by each use case, system architect can reasonable assign reliability index of system to each use case. This methodology based on use case can ensure the target of software reliability and provide reference for follow-up development and software test.

Key words: UML,Use case,Rcliability,Allocation