Abstract: By experiments,it is confirmed that ultrasonic action may raise the emanation of rock to a higher level; the emanation is more obviouslsly increased,when undergoing ultrasonic vibration each time A quantitative analysis of fracturing characteristic of rock after ultrasonic vibration (u.v.) has been made for the first time by a Magiscan Type 2 image-analysis system,obtaining a clear positive correlation between the degree of microfracturing and the times of u.v.; thus it is affirmed that there is an essential relation between anomalous behavior of emanation and microfracturing characteristics of rock under ultrasonic action. This paper also discusses on the basis of experiments that rock did not increase its emanation ability.,though microfracturing that occurred in it after u.v.; and emanation intensity can not be regarded as criterion for forecasting earthquake magnitude.