Abstract:A new method is presented for measurement of in-situ stresses at great depth,which is based on the experimental research on anisotropy of acoustic velocity and Kaiser effect of acoustic emission for deep formation cores. The different magnitude of acoustic velocity around the surface of core cylinder is caused by the different degree of unloading on the core. The magnitude of acoustic velocity is the minimum in the direction of maximum in-situ stress,and the maximum in the direction of minimum stress. Based on this principle,the relative position of the maximum and minimum horizontal principal in-situ stresses can be determined. Then the acoustic emission experiments are performed on the two core samples drilled from the certain position,and the horizontal in-situ stress state is determined. The advantage of this method is that the experiment can be performed on thin layer core instead of an integral core of 15 cm long without any fracture,and can improve measurement of in-situ stresses at great depth.