Objective To observe the short-term intraocular pressure after 25G+ pars plana vitrectomy (PPV) and analyze the possible influencing factors in rhegmatogenous retinal detachment (RRD) and proliferative diabetic retinopathy (PDR) eyes. Methods This is a retrospective case-control study. A total of 160 patients (163 eyes) of RRD and PDR who underwent 25G+ PPV were enrolled in this study. There were 88 males (89 eyes) and 72 females (74 eyes), with the mean age of (50.37±13.24) years. There were 90 patients (92 eyes) with RRD (the RRD group) and 70 patients (74 eyes) with PDR (the PDR group). Best corrected visual acuity (BCVA) and intraocular pressure (IOP) were performed on all the patients. The BCVA was ranged from hand motion to 0.6. The average IOP was (12.61±4.91) mmHg (1 mmHg=0.133 kPa). There were significant differences in crystalline state (χ2=9.285, P=0.009), IOP (χ2=58.45, P=0.000), history of PPV (χ2=4.915, P=0.027) and hypertension (χ2=24.018, P=0.000), but no significant difference in sex (χ2=0.314, P=0.635) and age (χ2=5.682, P=0.056) between the two groups. A non-contact tonometer has been used to measure IOP on postoperative day 1 and 3. The postoperative IOP distribution has been divided into five groups: severe ocular hypotension (≤5 mmHg), mild ocular hypotension (6 - 9 mmHg), normal (10 - 21 mmHg), mild ocular hypertension (22 - 29 mmHg), severe ocular hypertension (≥30 mmHg). Logistic regression analysis has been used to analyze the risk and protective factors. Results On the first day after surgery, there were 21 eyes (12.9%) in mild ocular hypotension, 96 eyes (58.9%) in normal, 22 eyes (13.4%) in mild ocular hypertension and 24 eyes (14.7%) in severe ocular hypertension. On the first day after surgery, there were 18 eyes (11.0%) in mild ocular hypotension, 117 eyes (71.7%) in normal, 23 eyes (14.1%) in mild ocular hypertension and 5 eyes (3.1%) in severe ocular hypertension. There was no significant difference of IOP distribution between the two groups (Z=−1.235, −1.642; P=0.217, 0.101). The results of logistic regression analysis showed that silicone tamponade was a risk factor for ocular hypertension in PDR eyes on the first day after surgery [odds ratio (OR)=15.400, 95% confidence interval (CI) 3.670 - 64.590; P＜0.001], while intraocular lens was the risk factor for ocular hypotension in PDR eyes on third day after surgery (OR=19.000, 95%CI 1.450 - 248.2; P=0.025). As for RRD eyes, the ocular hypotension before surgery was a risk factor for ocular hypertension on the third day after surgery (OR=3.755, 95%CI 1.088 - 12.955; P=0.036). For all eyes, silicone tamponade (OR=0.236, 95%CI 0.070 - 0.797), air tamponade (OR=0.214, 95%CI 0.050 - 0.911) and inert gas tamponade (OR=0.092, 95%CI 0.010 - 0.877) were protective factors for ocular hypotension on the first day after surgery (P=0.020, 0.037, 0.038); silicone tamponade was protective factor for ocular hypotension on the third day after surgery (OR=0.249, 95% CI 0.066 - 0.94, P=0.040); while aphakic eyes was the risk factor for ocular hypotension on third day after surgery (OR=7.765, 95% CI 1.377 - 43.794, P=0.020). The ocular hypotension before surgery was a risk factor for ocular hypertension on the third day after surgery (OR=4.034, 95% CI 1.475 - 11.033, P=0.007). Conclusions The abnormal IOP is common after 25G+ PPV with a rate from 28.3% to 31.1%. Silicone tamponade, air tamponade and inert gases tamponade are protective factors for postoperative ocular hypotension, aphakic eye is risk factor for postoperative ocular hypotension. Ocular hypotension before surgery and silicone oil tamponade are risk factors for postoperative ocular hypertension.