Objective: To investigate the effect of different anti-VEGF injection intervals before pars plana vitrectomy (PPV) on vitreoretinal interface microstructure modification and surgical outcomes in patients with proliferative diabetic retinopathy (PDR). Methods: A total of 120 PDR patients (120 eyes) scheduled for PPV received preoperative intravitreal injection of conbercept or ranibizumab. Using a representative sampling design, they were divided by the interval from the last injection to surgery: ≤3 days (observation group, 60 eyes) and ≥7 days (control group, 60 eyes). The proportion of the two drugs was balanced between groups. Posterior cortical vitreous detachment (PCD) grading, fibrovascular membrane characteristics, surgical performance indicators, complications, and postoperative best-corrected visual acuity (BCVA) were compared. Subgroup analyses by drug type were performed to verify consistency of effects. Results: The observation group showed significantly better PCD grade distribution: complete PCD (grade III) was 66.67% vs. 31.67% in controls (P<0.05). The proportion of atrophic/regressive fibrovascular membranes was 73.33% vs. 46.67%, while the fibroproliferative rigid type was only 6.67% vs. 31.67% (all P<0.05). Surgical time was shorter, fewer intraocular cautery applications were needed, and the incidence of iatrogenic retinal breaks was significantly lower (5.00% vs. 25.00%) (all P<0.05). Severe intraoperative bleeding rates did not differ significantly (5.00% vs. 13.33%, P>0.05). At 1 and 3 months postoperatively, LogMAR BCVA was significantly better in the observation group (all P<0.05). Stratified by conbercept and ranibizumab, these benefits persisted independently with consistent effect direction in each subgroup; all Breslow-Day interaction tests yielded P>0.05, indicating no drug type–by–interval interaction. Conclusion: Pre-PPV anti-VEGF injection with a short interval (≤3 days) effectively promotes complete PCD, induces benign fibrovascular membrane atrophy, and suppresses pathological fibrosis. This reduces surgical difficulty and iatrogenic injury risk, leading to better early visual recovery. The strategy shows consistent efficacy across conbercept and ranibizumab, representing a universally applicable optimized pretreatment regimen.