Objective To evaluate the development of white matter in preterm infants without brain injury by T2 weighted-fluid attenuated inversion recovery (T2WI-FLAIR) sequence. Methods The magnetic resonance imaging (MRI) and clinical data of 157 preterm infants without brain injury admitted to the neonatal intensive care unit of Qilu Children's Hospital of Shandong University from Jul. 2015 to Jul. 2018 and the corresponding data of 33 full-term newborns were collected. The preterm infants were divided into 5 groups according to the gestational age at birth:28-29, 30-31, 32-33, 34-35 and 36-37 weeks. Brain MRI with T2WI-FLAIR sequence was performed in preterm infants of each group within 1 to 3 days after birth and at 40 weeks of corrected gestational age, as well as in full-term newborns at 40 weeks of gestational age, measuring the maximum cross-sectional area and signal intensity ratio of low signal region in white matter. The differences of the maximum cross-sectional area and signal intensity ratio of low signal region in white matter were analyzed between the different gestational age groups and between preterm infants at 40 weeks of corrected gestational age in each group and full-term newborns at 40 weeks of gestational age. The differences of signal intensity ratios in the central, peripheral and adjacent ventricular regions of white matter in different gestational age groups were analyzed. Results The maximum cross-sectional areas of low signal region in white matter in preterm infants of 28-29, 30-31, 32-33, 34-35 and 36-37 week groups were decreased with the increase of the gestational age, the signal intensity ratios were increased with the increase of the gestational age (all P<0.01), and the signal intensity ratios were decreased in the order of occipital, parietal, frontal and temporal lobes (all P<0.01). The signal intensity ratios of low signal region in white matter with preterm infants in the groups of 32-33, 34-35 and 36-37 weeks were decreased in the order of central, peripheral and adjacent ventricular regions (all P<0.01). The maximum cross-sectional area of low signal region in white matter in preterm infants at 40 weeks of corrected gestational age was decreased significantly with the increase of the gestational age, and the signal intensity ratio was increased significantly with the increase of the gestational age (all P<0.01). The maximum cross-sectional area of low signal region in white matter of preterm infants in different gestational age groups at 40 weeks of corrected gestational age was significantly larger than that of the full-term newborns at 40 weeks, and the signal intensity ratio was significantly lower than that of the full-term newborns at 40 weeks (all P<0.01). Conclusion MRI with T2WI-FLAIR sequence can quantitatively evaluate the degree of myelination in preterm infants without brain injury, and it is an important non-invasive examination for the development of brain white matter in preterm infants.