Based on the characteristics of the emergency door on the wing of a civil aircraft, and its fault has a certain concealment, so it is particularly important to analyze its safety reasonably. The evaluation and selection principles of the latent failure of the emergency door are defined, and the exposure time of the latent failure is considered in the calculation of the failure probability of the bottom event. In addition, the fault tree of accidental opening of emergency door in flight is established. The bottom event of "the latch axis movement being not in place caused by tolerance accumulation", which is generally constructed, is considered as the mechanism movement is not in place caused by the joint action of tolerance accumulation and structural wear, which the modeling technology of bottom event is refined, and the reliability model is established in accordance with the engineering practice. The results of safety analysis before and after fault tree refinement are compared. The results show that the refined fault tree is more in line with the engineering practice and the safety analysis result of emergency door is more accurate.