The hazard assessment of debris flow was conducted by applying fault tree analysis(FTA) on characteristics of debris flow line engineering in subtropical area after analyzing influence factors of debris flow and the logical relationships between them. The new hazard assessment was applied to evaluate the hazard degree of 16 debris flow gullies in Lechang City of Guangdong Province. The results showed that it is more reasonable than the traditional grey correlation method because it solved some of the problems the traditional method always got such as the applying area was limited, the influence factors and weight were inflexible, and the non-linear relationship between them was not considered. Therefore, the fault tree analysis(FTA) was proved to be an effective and feasible method for the hazard assessment of debris flow.