Abstract: Objective: To evaluate the effect of different in-situ bone grafting methods on the healing of lumbar isthmus in adolescents, and to explore an effective method to promote the healing of lumbar isthmus. Materials and methods: from January 2015 to June 2019, 80 young patients with spondylolysis were analyzed retrospectively. The inclusion criteria were repeated low back pain with or without pain and numbness symptoms of lower limbs. The patients with lumbar isthmus were diagnosed clearly by imaging. The age was 18-35 years old. Strict conservative treatment was ineffective for more than 6 months. There was no lumbar spondylolisthesis or primary spondylolisthesis, no obvious disc herniation and nerve compression, single segment and bilateral isthmus. The imaging data were complete, and the follow-up was more than 6 months. Exclusion criteria: History less than half a year, unilateral isthmic fissure, age more than 35 years, isthmic fissure with more than two segments, combined with disc herniation and obvious nerve compression, lumbar spondylolisthesis more than 2 degrees, incomplete imaging data, follow-up less than 6 months. 80 patients were divided into two groups. Group A was treated with ilium autograft in isthmus and group B with ilium autograft and BMP autograft in isthmus. All cases were treated with isthmus debridement and bone grafting in situ, and pedicle screw fixation. The imaging methods included lumbar anterolateral film, flexion and extension lateral film, lumbar CT and sagittal reconstruction, and lumbar Mr. VAS was used to evaluate the improvement of lumbago and ODI was used to evaluate the improvement of function. The healing of isthmus was observed by CT and sagittal reconstruction. Three months, half a year, one year, one and a half years and two years after the operation, the clinical effect and isthmus healing were compared between the two groups. Results: compared with preoperative, vas and ODI of the two groups were significantly improved, but there was no significant difference in VAS and ODI between the two groups at different follow-up stages. In terms of isthmus healing, there were significant statistical differences between the two groups in three months, half a year and one year after operation, and group B was significantly better than group A. One and a half years after operation, there was no significant difference in the healing rate between the two groups. Conclusion: it is effective to promote the healing of isthmus by using in situ autogenous iliac bone graft and BMP.