Abstract:Hydraulic fracturing as a technique of geostress measurement has been widely used both at home and abroad due to its many outstanding merits. But this measuring method is only used to the 2D stress state in a plane normal to the borehole axis previously. The principle and method of 3D geostress measurement in three boreholes with different directions and one borehole have been suggested by YRSRI at home for the first time,expanding its applied scope,and it has been widely applied in engineering. Recently,a new measuring principle has been suggested by taking conventional hydraulic fracturing tests,at the same time taking reopening tests at one or more preexisting fractures,the 3D geostress state can be determined. It can be applied to measurement in depth borehole,and has wide prospects of engineering appliance. The calculating formulas of measured data processing of this method have been derived strictly. In the example,the results of 3D conventional hydraulic fracturing tests geostress measurement are checked not only by 2D stress state measured by conventional hydraulic fracturing technique in a plane normal to the borehole,but also by the 3D geostress states to be measured by over-coring stress relief method in corresponding depth in the same borehole.