As a standard object-oriented modeling language, UKL (unified modeling language) is lack of formal dynamic semantics. In this paper, an operational semantics for UML statechart diagrams is proposed according to UML1.1 specification documents. The formalization is able to deal with most of the features of UML statechart diagrams, which sets the basis for code generation, simulation and test cases generation. It has been used to generate test cases and to simulate the test process on platform of Rose98.