The major function of aircraft icing detection system was analyzed by FTA method. The FTA of icing detection system was built and simplified, and then the minimal cut sets were calculated and discussed here. According to qualitative results, the requirements of icing detection system on aircraft lever are suggested to avoid common cause Failures. The result analyzed by quantitative method is satisfied the requirement of icing detection system, which means the project of icing detection system is reasonable. The building and conclusion of FTA presented in this paper can be benefit for the icing detection system design．