Triaxial test is an important mechanical test in geotechnical testing and also in study of strength and constitutive relation. Soil test procedures put triaxial tests as the major experimental projects at home and abroad. Triaxial research and development of triaxial tests are carried out simultaneously. In light of the deficiencies of the existing triaxial apparatus a new triaxial apparatus controlled by hydraulic servo is introduced. The apparatus has a double pressure chamber, surrounded pressures inside and outside the chamber and axial loads is imposed by the hydraulic controller using servo stepper motor drives ball screw pushes the piston to produce hydraulic pressure. Volume deformation measurement is using a stepper motor servo ball screw piston movement displacement to calculate. Data acquisition is controlled by computer. Experimental results show that the deformation of the instrument and volume deformation is measured accurately; instrument system performance is stable. The new triaxial apparatus has the characteristics of a simple structure, easy to operate, the true state of stress, high degree of automation, low production costs, etc. It played a relevant role in promoting the popularity and development of triaxial tests.