Abstract: Through an important modification of the conventional triaxial compression ,a new triaxial apparatus was developed by Prof .Mogi about ten years ago .this devices has made possible to study the fundamental properties of rock deformation and fracture under the more general triaxial states of stress ,in which all three principal streets are different . In order to help the designing work of such apparatus to be carried out in China ,this paper presents in detail the bases of the modifications and structural features of the true triaxial compression apparatus .prof.Mogi’s advices about design and device developed in the institute are also given.