Objective　To simulate to two kinds of spinal manipulation that impose different torsion on isolated pig lumbar vertebrae.　Methods　Six fresh lumbar spine specimens from adult pigs were selected. Six loading programs were formulated by the usage of material testing system to stimulate oblique-pulling manipulation (no longitudinal traction and torques were 0,1,2 Nm respectively) and traction-rotation manipulation (longitudinal traction=250 N, torques were 0,1,2 Nm respectively). With the roles of the programs played on each specimen randomly, the biomechanical changes of porcine lumbar spine specimens caused by passive vertebral rotation were evaluated. It was achieved by measurement of changes of pressure in specimens' nucleus pulposus (L3/4) and in facet joints and disc height before and after the six programs. Results　(1) Pressure in nucleus pulposus：Changes of instantaneous value of pressure in nucleus pulposus: pressure elevated after oblique-pulling manipulation showed no statistical significance; pressure reduced after traction-rotation manipulation showed statistical significance (P=0.005); (2) Changes of disc height: compared with before, the changes of disc height in oblique-pulling group showed no statistical differences; however, disc height of traction-rotation group was higher than that of before, demonstrating statistical significance(P=0.001 ). (3) Results of pressure sensitive film: infrared scanning showed that pressure in facet joints could be elevated in both traction-rotation and oblique-pulling group, showing statistical significance (P<0.05). The larger the torque was, the higher the pressure was in facet joints. No statistical difference existed between traction-rotation and oblique-pulling groups.　Conclusions　 Pressure in nucleus pulposus could be elevated by oblique-pulling manipulation and reduced by traction-rotation manipulation. Under traction-rotation manipulation, the increase of torques had an effect on disc height. However, the increase was the most obvious without torques. Regardless of traction-rotation or oblique-pulling manipulation, the increase of torques could elevate pressure in facet joints.