Background: Moderate and late preterm infants account for 80% of preterm births, and their subtle brain developmental abnormalities are easily overlooked in clinical practice. Conventional imaging methods such as cranial ultrasound and MRI have limitations in dynamic and bedside monitoring. This study aimed to investigate early brain development in moderate and late preterm infants using resting state and music task functional near infrared spectroscopy (fNIRS). Methods: A prospective case control study was conducted, including 22 moderate and late preterm infants and 22 healthy term infants at 37–38 weeks of corrected or actual gestational age. fNIRS data were collected during resting and music stimulation conditions. Functional connectivity and hemodynamic responses were analyzed. Results: Results showed no significant differences in gender, Apgar scos, head circumference, and gestational age at examination between groups. Preterm infants had significantly lower birth gestational ageand birth weight. Resting state analysis revealed significantly reduced brain functional connectivity in preterm infants, mainly in the right hemisphere regions associated with language, executive function, and visual processing. During music stimulation, although average signal changes did not differ significantly , preterm infants exhibited flatter hemodynamic responses and weaker neurovascular coupling. Conclusion: This study demonstrates that moderate and late preterm infants present early impairments in brain functional integration and neurovascular regulation. fNIRS provides a simple, bedside, and objective tool for the early detection of concealed brain developmental abnormalities in this population.