Abstract: Evaluation is an important method for assuring ultra-high reliability of high dependable software.The past methods，either be not fit for characteristic of ultra-high reliability，or be not fit for the real evaluation.Based on actuality，the article introduces an evaluating method based on experience Bayesian deduce.The method not only makes use of the advantage of validate method of experience Bayesian deduce，but also combines the iteration theory of half search arithmetic.The two together achieves the real available evaluation of ultra-high reliability.The actual application implies that the method is feasible and impersonal，and having high applying value.