In view of spread strength of empennage during rocket flight, as the object on a rocket empennage, the analytical model of empennage spread was established on the theoretical analysis of empennage spread process. The relationship between spread angle and rotate speed of empennage with time during empennage spread process were obtained from the model, and the load condition of empennage was also obtained. Based on the load condition from the analysis results, the stress responses of two different-structure empennages impacting on empennage seat when deploying were analyzed by numerical simulation. The analytical results were validated by exterior ballistic flight test. As a result, the results of analysis show good agreement with the test results.