During the execution of real-time software, a sequence of events due to time takes place between the concurrent processes. Because of the un-predictability of concurrent processes, multiple executions of real-time software with the same test cases may produce different results. This non-deterministic execution behavior always creates problems in real-time software testing. This paper explores real-time software testing, which combines decomposition of Petri nets model with expansion of its time criterion. It includes (1) guideline of how to handle the non-deterministic properties of real-time systems using time Petri nets model, (2) the rules of how to decompose the Petri nets model into independent segment groups, and (3) the way test cases are generated using independent segment group and time variation method.