Some researchers carried out the microwave detecting experiment of loaded rock, and found the microwave radiation changing significantly when the rock fractured, which indicates that the passive microwave is possible to detect the phenomenon of rock fracture and failure, including earthquakes. But it is unclear by now about the patterns and rules of microwave radiation variation in rock fractures, and the theoretical foundation is also unclear. In this paper we first analyze the microwave radiation characteristics and the influence factors of fractured rock based on the microwave radiation theory of layered medium, and the microwave radiation feature is compared with that of intact rock. Then the theoretical analysis results are verified by a series of passive microwave detecting experiment of fractured rocks.