The complex and uncertain relationship among failures was always ignored in failure sample selection based on traditional testability demonstration experimental method. A failure pervasion model is founded based on fuzzy probability Petri net (FPPN) which can depict the propagation and pervasion relation among failures, then failure pervasion intensity is defined, the process of failure pervasion was depicted based on k-step fault pervasion algorithm and the pervasion intensity was expressed by a value. The method of sample selection based on failure pervasion intensity and failure rate is introduced into the process of sample selection. The practical application shows that the sample set selected based on failure pervasion intensity and failure rate can represent the failure set adequately.