Abstract: Analysis of fuzzy reliability based on cloud models in aircraft navigation system is expatiated in this paper. A new mathematical representation of qualitative concepts is represented by cloud models. With the new models, mapping between qualities and quantities becomes much easier and interchangeable. They integrate fuzziness and randomness using digital characteristics, such as expected value Ex, entropy En and hyper entropy He. The fuzziness and randomness are not only complementary, but also inseparable. The application of cloud models to fuzzy reliability analysis and fault detection in aircraft navigation system can effectively enhance reliability assessment of navigation system. The simulation results demonstrate that the method has certain validity and feasibility.