Abstract: The spine manipulation of traditional Chinese medicine treats the degeneration of the lumbar intervertebral disc by applying transient distraction and rotation forces on the lumbar spine. In this paper, numerical simulation considering fluid-structure interaction is used to study the underlying biomechanical mechanisms. Through experimental measurement and literature research, reasonable parameters of distraction and rotation loads have been determined. A method is developed to build a detailed geometric model of lumbar spine, which uses data from computed tomography scans of human body and anatomical knowledge. Cancellous bones, endplates, and intervertebral discs are considered as poroelastic materials, while others are considered as linear elastic materials, in order to consider the effect of fluid-structure interaction in biological tissues considered here. Through numerical simulations, the stress, strain and fluid flow in the intervertebral disc under transient loads and their combination are obtained. It is found that the transient load generates fluid flow in the nucleus pulposus by changing the stress of the solid matrix of the L4/L5 intervertebral disc and producing pressure gradient across the nucleus pulposus. Distraction causes the fluid to flow out of the nucleus pulposus first and then flow into the nucleus pulposus to produce a change of water content. Under clockwise rotation, opposite flow processes occur on left and right sides of the nucleus pulposus. Water content on the right side of the nucleus pulposus changes greater than the left side. The method used in this research provides a new method for the study of the pathophysiological mechanism of human intervertebral disc degeneration related to the flow process. This method also provides a pathway to make the spine manipulation of traditional Chinese medicine scientific. An entry point is provided additionally for the related study of mechanical and biological coupling study, as well as the basic research of nucleus pulposus regeneration.