Objective To observe the best time of application of conbercept before vitrectomy for proliferative diabetic retinopathy (PDR). Methods The data of 75 eyes of 75 cases of proliferative diabetic retinopathy who underwent vitrectomy from May 2017 to Jul. 2018 were retrospectively analyzed. All cases were divided into two groups randomly. Group A , 38 eyes of 38 cases, received intravitreal injection of Conbercept at 7 days before operation, and group B, 37 eyes of 37 cases, received intravitreal injection of Conbercept 3 days before operation. The operation time, intraoperative and postoperative complications and the visual acuity at 6 months postoperatively were observed and compared between the two groups. Results Postoperative visual acuity of the two groups were significantly improved (t=8.854, P=0.000). Postoperative recurrence of vitreous hemorrhage occurred in 1 eye (2.6%) of group A and 7 eyes (18.9%) of group B (P=0.028). Postoperative intraocular hypertension occurred in 5 eyes (13.2%) of group A and 7 eyes (18.9 %) of group B, the difference was not statistically significant (χ2 =0.463, P=0.496). The difference were not statistically significant between the two groups in operation time, intraoperative retinal hemorrhage, iatrogenic tear incidence, silicone oil or gas tamponade rate (P=0.502, 0.518, 0.304, 0.444, 0.720). Conclusion Application of Conbercept before vitrectomy can improve the visual acuity for patients with PDR. The incidence of vitreous hemorrhage in patients applicated of Conbercept at 7 days before vitrectomy can reduce the incidence of vitreous hemorrhage than that in patients applicated of Conbercept at 3 days. Key words: Conbercept, intravitreal injection; Retinopathy, proliferative diabetic; Vitrectomy