Objective To establish the three-dimensional finite element model of lumbar spine(L) 3-5 segments of the normal spine of 14-year-old adolescents to analyze the biomechanical changes of the lumbar spine after different degrees of lumbar foraminal plasty, and to provide reference for improvement of adolescent foraminoplasty.   Methods A14-year-old female volunteer with no previous history of lumbar spine was selected to collect lumbar CT image data and we imported it into Mimics 16.0 software for modeling. ABAQUS software was used to conduct finite element model force analysis. Models M1 (1/4 of the left superior facet area of L5 was removed), M2 (1/3 of the left superior facet area of L5 was removed) and M3 (1/2 of the left superior facet area of L5 was removed) were established on the basis of the normal vertebral column L3-L5 segment model M. The stress of facet joints of corresponding segments was measured and compared under six loading conditions, such as neutral position, forward flexion and extension.   Results The established three-dimensional finite element model and variance analysis model were effective. There was a statistically significant difference between the stress value of L5 in model M1 and that in model M under loading conditions of extension and right-rotation of the left superior articular process (P< 0.05). The stress value of L4 left superior articular process in model M2 under left flexion and loading condition was significantly different from that in model M (P<0.05). The model M3 L4 in the upper left articular process in the condition, L5 upper left articular process in a left turn, bow, bow on the right side, right the upper right of the L4 joints on the right side bends, right rotation condition, the upper right of the L5 joints in the stretch, left flexion, left rotating under the condition of loading stress value compared with model M articular process stress value difference was statistically significant (P<0.05).   Conclusion In adolescent foraminoplasty, the lumbar biomechanical stability is obviously damaged when the medial area of the superior facet of one side and one segment is excised. It is recommended to carefully remove the facet facet of more than 1/2 in clinical practice to avoid lumbar instability.