Objective To investigate the efficacy and safety of stereotactic body radiotherapy （SBRT） combined with sintilimab and bevacizumab in the treatment of patients with unresectable hepatocellular carcinoma （uHCC） and related prognostic factors. Methods A total of 42 patients with uHCC who underwent SBRT combined with sintilimab and bevacizumab in Department of Radiation Oncology， The Fifth Medical Centre of PLA General Hospital， from March to December 2022 were enrolled. The prescribed dose of planning target volume was 36‍ ‍—‍ ‍50 Gy in 5‍ ‍—‍ ‍6 fractions for continuous irradiation， followed by the regimen of sintilimab and bevacizumab. Each course of treatment was 3 weeks until the presence of tumor progression or serious adverse events. The Kaplan-Meier method was used to calculate overall survival （OS） rate and progression-free survival （PFS） rate， and the log-rank test was used for comparison between groups； the Cox proportional hazards model was used to investigate the influencing factors for prognosis. Results The median follow-up time was 21.6 months， with an objective response rate of 69%， a disease control rate of 85.7%， a median PFS of 10.0 months （95% confidence interval ［CI］： 6.7‍ ‍—‍ ‍13.0）， and a median OS of 23.3 months （95%CI： 14.7‍ ‍—‍ ‍31.8）. Most adverse events were grade 1‍ ‍—‍ ‍2 events， and there were no fatal adverse events. At 6‍ ‍—‍ ‍8 weeks after treatment， the AFP response group had a significantly better OS than the non-AFP response group （not reached vs 11.8 months， P=0.007）. The multivariate analysis showed that AFP response was associated with the good prognosis of patients （hazard ratio=0.31， 95%CI： 0.13‍ ‍—‍ ‍0.75， P=0.009）. Conclusion For patients with uHCC， SBRT combined with sintilimab and bevacizumab can improve survival with a manageable safety profile， and a >50% reduction in AFP at 6‍ ‍—‍ ‍8 weeks after treatment can be used as a potential prognostic indicator.