Since half century,the unsolved principal questions in geostress measurement using borehole method are hypothesizing that the mech-anical property of rocks is isotropic,unthinking the borehole effect,unconsidering the measuring time effect and simplifying the changeful mechanical property of rocks.The maximum synthetic error caused by them can be up to 100% of principal stress value and 90° in principal stress orientation and the error can result in that the principal stress property may change from positive to negative.For purpose of high level geostress measurement,the measurement must be based on aniso-tropy of mechanical property of rocks;the borehole effect must be subtracted or avoided;the time effect in measurement be avoided or considered;the effect of changeability of mechanical property of rocks be avoided in the geostress measurement.The each component of geos-tress must be measured respectively and the fixed longterm continuous observation be made.