Abstract: The relation model of failure modes and characters of the unit under test (UUT) is created. The general adequacy criterion for the sample set is proposed according to the relation model. Based on the general adequacy criterion, the new method for determining the demonstration’s plan is studied, which includes the methods for determining sample size and creating sample set and the pass judgement. A case shows the feasibility of the new method. Comparing with the exist methods, the new method is more suitable for the exist state of the testability requirements and the integrative demonstration of multiple testability requirements, and the created sample set can coverage the important character of UUT.

Key words: adequacy criterion, testability demonstration, plan, sample size, failure mode