Real-time embedded software, such as the navigation and the flight control syst ems, requires large amount of testing to measure their reliability according to the ultra-high reliability requirement. A united model language(UML)-based rel iabilit y test data generation method for real-time embedded software was presented, wh ich consists of use-case profile, interface model and test data model. The so ftware functions tested was analyzed by a use-case frofile; The interface of em bedded software was described by an interface model; The sof tware operational profile was depicted by a test data model. Based on the three models, the reliability test data for the real-time embedded software can be generated b y random sampling. With this method, the tool for software reliability test data generation can be developed and this method is of practical value in soft ware reliability testing.