Abstract: This paper illustrated experimental study on the influence of ultrasonic vibration upon microstructure and emanation process of saturated rocks. It was found by scanning electron microscope observation that specimens under ultrasonic vibration, whether on the ultrasonically irradiated sides or on the non-ultrasonically irradiated sides, all show a large number of fissured traces, i. e. microcracks. So it can be inferred that under the ultrasonic vibration the development of microcracks provided an outward-diffusing "passage" for the sealed radon to take part in the emanation process.The results of the ultrasonically vibrating experiments indicate that the ultrasonic vibration made the amount of radon separating-out of rock obviously increased, and the amount would be as much as it was before vibration when the vibration stopped. The increment of separating radon depends on the times of ultrasonic vibration. These results obtained are consistent with the scanning electron microscope observation showing that the primary rock structures were certainly destroyed by ultrasonic vibration. During each vibration, new cracks appeared and the separating amount of radon was also increased correspondingly. For the first vibration, the amount of radon increased by a factor of 4.5 under the temperature-control condition (it will be 4.3 under temperature-uncontroi event). For the fourth vibration, it increased by a factor of 9.1 under temperature-control condition (it will be 11.2 under temperature-uncontroi condition). Among the increment of radon, absorbed radon accounts for 64-76 percent, sealed radon accounts for 24-36 percent. The contribution of the ultrasonic thermal effect to the separating radon accounts merely for 10-30 percent.The experiment results show that the rock emanation process was clearly related to the ultrasonic vibration. Its mechanism is rather complicated. It is reasonably considered that prior to the failure of rock the expensive microcracking produced accoustic emission, i. e. ultrasonic vibration, leading to a constant emanation from rocks in a significant amount which may be probably regarded as a precursory information of radon.