Abstract: To solve the problem of huge graphic user iuterface (GUI) elements’ states and complicate combination of user operation, a GUI test model based on extended place/transition system for specific GUI software was proposed. In the model, places represented type of user operation, and transitions represented user operation. Based on the model, three GUI test coverage criteria, were designed and test coverage based on places, test coverage based on transitions and test coverage based on transition-pairs, were put forward. The differences between the last and event-pair coverage was analyzed. The related test generation algorithm was designed. Experiment result of calculation shows that the transition-pair coverage has the same effectiveness in fault finding as the event-pair coverage, but the number of generation test suits is only about 40%.