Abstract: Rock mechanics experiments, especially those for determination of rock deformation characteristic, are deeply affected by the stiffness of a testing machine. In order to reveal the true mechanical properties of rock, some steelbars parallel to the specimen are used to increase effective stiffness of experiment system. Stiffness experiment system and load-displacement measurement system are designed for disc splitting test, and complete stress-strain curves of marble disc are obtained. Finally, some factor affecting experimental results are discussed.