Objective To study the stability of upper lumbar vertebra in spondylolysis by measuring the upper vertebra pressure on lumbar spondylolysis models. Method Nine freshfrozen human lumbar spinal specimens were used as experimental models. The pressure on upper vertebral discs of lumbar vertebrae was measured by the material testing machine (MTS858 Bionix test system)with extension, flexion and axial, bilateral compression being applied on two groups of specimens: 1) intact spine; 2) lumbar spondylolysis. Results Compared with the intact specimens, the pressure of upper lumbar vertebra in spondylolysis was increased by 1.3％，1.5％，1.7％ in axial compression with 600, 800, 1 000 N (the differences were not significant (P＞0.05)), by 20.97％，24.45％，28.79％ in 15°of extension with 300, 500, 700N (the differences were significant (P < 0.01)), by 14.15％，17.86％，24.92％ in 15°of flexion with 300, 500, 700N (the differences were significant (P < 0.01)), by 3.54％，2.12％，1.14％ in 15°of bilateral compression with 300, 500, 700N (the differences were not significant (P＞0.05)). Conclusions Lumbar spondylolysis has a significant mechanical influence on lumbar spine not only at the involved level but also at the upper adjacent level, which can affect the stability of lumbar spine correspondingly.