Objective To compare the efficacies and prognoses of stereotactic radiosurgery and fractionated stereotactic radiosurgery in treatment of brain metastases of lung cancer with diameter of 3-7 cm.Methods A retrospective study of 80 patients with brain metastases from lung cancer with diameter of 3-7 cm treated with gamma knife in our hospital from April 2010 to November 2016 was performed.There were 46 patients in stereotactic radiosurgery group and 34 in fractionated stereotactic radiosurgery group.The local tumor rate,incidence of complications,changes ofperitumoral edema,and Kamofsky Performance Status (KPS) scale scores at 3 months after operation were compared between the two groups.Multi-factor Cox regression model was used to analyze the factors influencing the short-term efficacy of patients.Kaplan-Meier survival analysis was used to evaluate the survival rate of patients.Results Three months after operation,the local tumor control rate and incidence of complications were 73.9％ and 21.7％ in the stereotactic radiosurgery group,and 94.1％ and 2.94％ in the fractionated stereotactic radiosurgery group,with significant differences (P＜0.05).As compared with those in the stereotactic radiosurgery group,the percentage of patients with increased grading ofperitumoral edema was significantly decreased and percentage of patients with increased KPS scores was significantly increased in fractionated stereotactic radiosurgery group (P＜0.05).Multivariate Cox analysis showed that tumor diameter was the only statistically significant risk factor for prognosis (P＜0.05).The median survival time was 13.6 months in the stereotactic radiosurgery group and 16 months in the fractionated stereotactic radiosurgery group.The one-year survival rate and accumulate survival rate showed no significant differences between the two groups (P＞0.05).Conclusion As compared with stereotactic radiosurgery therapy,fractionated stereotactic radiosurgery has more advantages in the treatment of lung cancer brain metastases with diameter of 3-7 cm.