<正> Selection of test cases plays a key role in improving testing efficiency. Black-boxtesting is an important way of testing, and its validity lies on the selection of test cases insome sense. A reasonable and effective method about the selection and generation of test cases isurgently needed. This letter first introduces some usual methods on black-box test case generation,then proposes a new algorithm based on interface parameters and discusses its properties, finallyshows the effectiveness of the algorithm.