Abstract The experimental results of rock specimens in laboratory are dispersive to identify the property of rock mass. The Young′s modulus is various with the definition method. Specimens from rock strata are of micro-fissures resulting from the triaxial extension effect in drilling process. The fissures will close and slip at the initial step of uniaxial compression，which causes large amount of axial deformation. So the secant modulus from zero stress can not describe the deformation property of the practical rock mass. The average modulus，which is determined from the average slope of the more-or-less straight-line portion of the axial stress-strain curve，is less influenced by the experimental conditions. But the calculation method is not clear. In this paper，the maximum secant modulus is suggested，which is the maximum of all secant modulus with stress difference of 50% strength of the specimen. And also，the specimens from rock core are contacted in line，so it is better to use the harmonic average of specimens′ modulus，not the arithmetic average，as the mean modulus of the rock stratum. The harmonic mean method of Young′s modulus can express the great influence of soft seam on the deformation property of the whole stratum.
