Abstract: Acoustic emission (AE) will occur if the rock mass is under external pressure. The reason of AE is studied here. On the basis of some previous work, a finite element simulation of slotted rock mass is performed and the stress distribution is given. By identification of stress distribution and AE location it is found that the shearing stress is the main reason of the AE events either in uniaxial tests or in confining tests. The events caused by shearing stress account for about one half to two thirds while those caused by normal stress are much less.