Three dimensions finite element model of lumbar inter-body fusion was established to analyse internal biomechanical responses of lumbar inter-body. Single inter vertebrae fusion was performed and fixed with pedicle screw then we observed stresses distribution of lumbar and analysed degeneration mechanism of the neighboring inter-vertebrae joints. The study provided some information on the design and application of spinal internal fixation devices. At the same time we indroduced a model on studies of the lumbar fusion and fixation.