Objective To evaluate the diagnostic value of CT in the spondylolysis of lumbar spine and improve the technique of CT scan.Methods The CT appearances of the spondylolysis of lumbar spine were analyzed in 20 cases.Results CT could demonstrate the spondylolysis and its abnormal features that led to compress nerve root.Conclusion CT scan plays an important role in the diagnosis of the spondylolysis of lumbar spine and in selecting treat methods.Technique of CT scan improved can depict the specific feature of spondylolysis truely.