Abstract：Rocks are different in their structure，mineral particles and deforming history，and the effect of confining pressure on Young’s modulus is not understood clearly. The Young’s modulus is various with the definition method as the stress-strain curve is not a direct line. The secant modulus from zero stress can not describe the deforming property of the practical rock mass. But 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. Experimental results from servo-controlled testing machine and public references are used to study the relation between confining pressure and Young’s modulus for various rocks. Confining pressure does not influence Young’s modulus of rock with homogeneous material in macrostructure or with local flaw only. But specimen from weathered rock or drilled in weak rock strata usually has distributed fissures. The friction in the fissures will increase with confining pressure，which reduces the shear slide between fissures and makes Young’s modulus higher as well. The relation between Young’s modulus and confining pressure shows the state of rock damage.
