A lot of prior information in complex system test has been accumulated. To use the prior information for complex system testability quantitative analysis, a new complex system testability modeling and analyze method based on Bayesian network is presented. First, the complex system’s testability model is built using various kind of prior information by Bayesian network learning algorithm. Then, the way of assessing the testability of complex system is provided using the inference algorithm of Bayesian network. Finally, some proper examples are provided to prove the method’s validity.