Abstract: In order to study the Felicity effect of carbon/epoxy composite, the test program of carbon/epoxy composite ［0］ unidirectional plate was developed, and then the experiment data was analyzed to study the composite Felicity ratio variation law. The results showed that the composite Felicity ratio tends to be smaller when the damage degree is getting severer, which means that the Felicity ratio can evaluate the damage degree of composite very effectively.