Abstract: According to the SMP criterion, the ratio of shear stress to normal stress on SMP plane in entity space is employed to determine whether or not the soil sample is damaged. Under triaxial compression and triaxial extension conditions, the SMP criterion degrades to the Mohr-Coulomb one. By analyzing the stress state of a general plane in a cubic soil element under three principle stresses, the location of SMP plane is discussed, and the stress state of the SMP plane is also deduced. After these, the determination procedure of SMP state point in Mohr’s stress circle is introduced.