Safety analysis is one of the most important means of compliance demonstration for airworthiness regulation. Fault tree analysis(FTA) and Markov(MA) models are widely used in safety analysis. In this paper, we address the application of FTA and MA model in failure sequence dependent event. The results of FTA are compared with that of MA model. It shows that if the system is composed of items with active failure(λ×t is minor) ,using either FTA or MA model, we can correctly obtain system failure probability. In addition, we find using FTA analysis could reduce the calculation complexity. However, if the system is composed of items with potential failure, due to the long exposure time (λ×t is major), MA model could be used to analyze system safety more accurately. More detailed analysis indicates that the quantitative analysis of the degree of importance for the top event can be used to establish the system repair method.