Abstract: Objective: To investigate the risk factors of bone nonunion after posterior lumbar interbody fusion. Methods: The case data of 218 patients who received posterior lumbar interbody fusion and followed up for one year were retrospectively analyzed.The patients were divided into bone graft nonunion group (n=25) and bone graft fusion group (n=193) according to dynamic X-ray.The lumbosacral fusion,number of fusion segments,operation mode,fat rate of multifidus and erector spinalis,and bone mineral density of patients were collected for univariate analysis and multivariate logistic regression analysis.Subgroup analysis was performed on the number of fusion segments.The ROC curve was used to determine the high-risk cutoff point. Results: Univariate analysis showed that there were differences in the number of fusion segments,lumbosacral fusion,fat infiltration rate of multifidus muscle and preoperative bone density between the two groups (P<0.05).Multivariate logistic analysis showed that lumbosacral fusion,multi-segmental fusion,high fat infiltration rate of multifidus muscle and preoperative bone mineral density were independent risk factors for nonunion of bone graft after lumbar fusion (P<0.05 to P<0.01).Subgroup analysis showed that the fat infiltration rate and bone mineral density were the independent factors for bone graft nonunion patients with single segment fusion (P<0.05),and the number of fusion segments,lumbosacral fusion,fat infiltration rate of multifidus muscle and bone mineral density were the independent factor for bone graft nonunion patients in multi segment fusion (P<0.05).ROC curve andysis showed that when fat infiltration rate of multifidus muscle was more than 22.75% and bone mineral density was less than -0.85,the risk of nonunion of intervertebral bone graft was higher. Conclusions: Preoperative fat infiltration of multifidus muscle and osteoporosis are closely related to bone fusion after posterior lumbar interbody fusion.Orthopedic doctors should pay attention to the above situations,especially for patients who need long segment lumbosacral fusion.