This is an unmasking randomized clinical trial. the main purpose of this study is to analyze whether posvitrectomy proactive use of conbercept can reduce the rate of postoperative complication in PDR patients.

Inclusion Criteria:

• PDR patients undergoing vitrectomy

Exclusion Criteria:

• patients who had received intravitreal injection or systemic use of all types of anti-VEGF agents in the recent three months before vitrectomy
• patients who had received intravitreal injection or systemic use of all types of steroid in the recent one month before vitrectomy
• patients who had received complete PRP before vitrectomy
• patients who are pregnant