A triaxial unloading experimental method fitting the process of stress changes in engineering practice such as underground openings or mine slope stability is proposed. The surplus strength with cleer for interpretation of data. It is found that through such a test there are unique features of deformation during simultaneous unloading of longitudinal and transverse stresses

which indicates that it would be necessary for mechanical properties of rock mass by using loading process coincident with the stress changes in geotechnical engineering.