Aircraft icing will cause a series of problems such as aerodynamic performance degradation and flight quality degradation of the whole aircraft, which will pose a great threat to flight safety. Modern civil aircraft are generally equipped with ice detectors to deal with the problem of icing in flight. The ice detection system sends an ice warning to flight crew to help them determine the time of activating the anti-ice system. This article first introduces the fault tree analysis characteristics of civil aircraft ice detection system. Then based on the functional requirements of ice detection system, a preliminary architecture design is carried out for the ice detection. Then fault tree analysis is used to analyze the failure probability of the main failure mode of the ice detection system. During the process, it is found that the failure probability of the preliminary architecture's failure mode is far from meeting the system requirements. Finally, redundant design is carried out on the system architecture to ensure that it meets the safety requirements of the system.