Purpose: To evaluate the rate of and time to complete vascularization in premature infants and to explore associated factors. Methods: A monocentric, retrospective cohort study including 541 premature infants who underwent screening for retinopathy of prematurity (ROP) between July 2016 and June 2019. Patients underwent regular dilated fundus examinations with indirect ophthalmoscopy until complete vascularization. The worse eye of each patient was included for analyses. The proportion of infants with complete retinal vascularization at the last visit and the time to full vascularization was analyzed. Results: Among all infants (average gestational age 31.29 ± 3.12 weeks), 490 (90.57%) had complete records of retinal vascularization outcomes, of whom 439 (89.59%) achieved complete vascularization. The average postmenstrual age for complete vascularization was 45.39 ± 11.04 weeks, and 95.22% achieved completion before 64 weeks of postmenstrual age. Retinopathy of prematurity developed in 118 (22.56%) infants; 33 (6.10%) received antivascular endothelial growth factor treatment. For all infants screened for ROP, lower birth weight, presence of ROP, and antivascular endothelial growth factor therapy predicted delayed complete vascularization; for infants diagnosed with ROP, only lower birth weight predicted delayed complete vascularization. Subgroup analysis showed significant differences between patients without ROP, with untreated ROP, and with treated ROP in time to complete vascularization and its rate (99.7%, 66.2%, and 16.7%, respectively). Conclusion: Lower birth weight predicted delayed complete vascularization. Antivascular endothelial growth factor therapy and the presence of ROP, including ROP severity, may also affect time to complete vascularization. These findings should help improve the understanding and management of persistent avascular retina in preterm infants.