Abstract: Hollow inclusion strainmeter, a new stress-measuring equipment of rock mass in situ, is presented in this paper. The design philosophy, work principle and the method of calculation are explained in detail. The examination of comprehensive error in laboratory and testing study in situ are described with satisfying results. The hollow inclusion strainmeter can measure three dimensional stresses of rock masses in a borehole and seems far better than the other kind of stress-measuring equipment in situ, especially in weak or broken rock masses.