Objective To observe the effect of platelet-rich plasma (PRP) gel combined with local decompression bone grafting on lumbar fusion. Methods A total of 80 patients with lumbar degenerative diseases who needed posterior lumbar fusion surgery at Mianyang Orthopedic Hospital between January and June 2024 were selected and randomly divided into groups A and B using the random number method. For patients in group A (n=40), decompression bone graft combined with PRP gel was implanted intraoperatively, while those in group B (n=40) received only decompression bone graft. The Visual Analogue Scale (VAS) pain scores before surgery and 3 days, 1 month and 3 months after surgery, the Oswestry Disability Index (ODI) and the Activities of Daily Living (ADL) scores before surgery and 1 month and 3 months after surgery, the intervertebral space height before surgery and 1 month and 3, 6, and 12 months after surgery, and the intervertebral fusion rate 3, 6, and 12 months after surgery were observed between the two groups. Results The VAS, ODI and ADL scores of group A were significantly better than those of group B 3 months after surgery (P<0.05). Regarding the intervertebral space height, the interaction effect of time and group was statistically significant 6 and 12 months after surgery (P<0.05), and the intervertebral space height of group A was better than that of group B at these time points (P<0.05). The difference in fusion time survival curves between the two groups was statistically significant (P=0.008), group A was better than group B. Conclusion Intervertebral bone grafting with PRP gel mixed with local decompression bone can significantly increase the intervertebral fusion rate, reduce the degree of intervertebral space subsidence, and significantly improve the postoperative pain and quality of life of patients, providing an effective and feasible new strategy for improving the intervertebral fusion rate after lumbar fusion surgery.