Objective To develop a biomechanical model of bone graft fusion of bilateral articular process combined with spinous process using 3D finite element method to explain its preventive role on postoperative correction loss for thoracolumbar fracture surgery, and to evaluate the effect on preventing postoperative correction loss than that of bone graft fusion simply in bilateral facet joints. Methods Computed Tomography (CT) scans were performed on L1-2 motion segment of the fresh spine specimen of an adult male cadaver, and mechanical model of functional spinal unit of L1-2 with vertebrae fracture affiliated disc serious damage were developed by defining injuried material properties. From simulating to dismantle internal fixation in patients who were dealed with bone graft fusion either of bilateral articular process combined with spinous process or simply in bilateral facet joints, two digitized surgical models were established by finite element method in Ansys 11.0 software platform. Four load conditions containing compression, anteflexion and retro-extension were added on digital fusion models on the basis of three-column spine theory to compute stresses/strains in bone graft and endplates and compressive displacements in damaged discs. Rusults Under the action of compressive load, anteflexion moment or post extension moment, the vertical compressive displacement and strain of disc annulus fibrous of the new fusion model (FSF) reduced significantly than those of the old one (FF), about 20%-35%; and the stress level of bone graft of articular process decreased too, about 5.5%-13%. The bearing capacity of bone graft between spinous process increased markedly up to 2.5-12.3 times or more than that of the interspinous and supraspinous ligaments. Conclusion After the fusions between the bilateral facet joint and the spinous process, the load bearing function of the spinal column is carried out mainly by three points of the spinous process and bilateral facets in three–dimensional space, and a new strengthening tension-band is formed by transplanted bone between spinous process. It can increase the three-dimensional stability of spinal segments, effectively relieve the stress concentration on the bone graft area of bilateral articular process, reduce the vertical compressive strains and displacements of the acutely injured disc, and can prevent the loss of postoperative correction for thoracolumbar fracture surgery.