Abstract: It is a fundamental problem of the rock mechanicalmeasurements in material testing machine how to measure the rockdeformation exactly. Rock uniaxial compression tests were carried out in twodifferent testing machine so as to investigate the effect of machinestiffness on the deformation measurement. The energy transfer and conversionof testing system and sample during the loading and unloading processes areanalyzed in this paper. It is found that the elasticaccumulation energy of material testing machine affects the mechanicalmeasurement of rocks. Moreover a revised method is proposed which can beadopted to calculate the deformation of rock during the test.