For now,the strainmeters used are equipped with electrical sensors which are susceptible to electromagnetic interference,difficult to remove the z ero drift and inaccurate caused by annual drift,so we develop a borehole strainmeter based on fiber Bragg grating (FBG).A curve-side-triangle structure used as the strain gauge is designed by finite e lement analysis software. The gauge is encapsulated by a stainless steel cylinder.The problem of cross-s ensitivity of FBG sensor is resolved though the method of reference grating.Two gratings are fixed on th e gauge.One is used for temperature compensation,while the other measures the strain.In order to si mulate the environment in the borehole,a microstrain platform is established,where the borehole strai nmeter′s feasibility is tested.Experimental results show that the strain sensitivity is 0.0923pm/με and can be improved greatly.