Abstract: Test cases generation is a key technique of software testing. In this paper, a test cases generation method for UML statecharts is described according to its hierarchy and concurrency. It begins with the generation of test cases bases of main UML statecharts and sub UML statecharts considering all composite states as basic ones, and then generates the test cases of the whole UML statecharts according to some merging rules and Wp-method. This method supports the incremental test cases generation. Theory and experiments show that the cases suites guarantee full coverage and the methods generate less test cases if it satisfies some assumptions. The improvement is very useful to large systems and to building automatic test tools.