Objective.This paper aims to explore the influence of nucleus pulposus on the biomechanical behaviors of a Lumbar Motion Segment.Our results could assist spine care professionals in providing convincing recommendations to their patients.Methods.On the basis of a L4-L5 segments finite element model that is built according to CT radiological data of a healthy adult, we reconstructed three models of mildly herniated disc and three of severely herniated disc.We removed the nucleus pulposus (NP) of the discs from the models (Step 1), and then filled nucleus cavities with one material which Poissons ratio and elastic modulus are 0.3 and 3 Mpa respectively (Step 2).The biomechanical characteristics of our models were simulated using finite element method (FEM) under five loadings: axial compression, flexion, lateral bending, extension and rotation.We mainly focused on the change of four characteristics related to biomechanical behaviors after the removal of NP and nucleus cavity being filled: the rotation degree, the maximum stress in annulus fibrosus, the facet contact forces and the maximum deformation.Results.After the removal of NP, the rotation range, the maximum stress in annulus fibrosus (AF) and the facet contact forces were increased, while the maximum deformation of discs was decreased.After the nucleus cavities were filled, the rotation degree, the maximum stress in AF and the facet contact forces were decreased and the maximum deformation in disc was increased.Conclusions.The removal of NP can impair the stability of lumbar, while filling the nucleus cavity helps to restore the stability of lumbar and prevent disc herniation from further aggravation.