Background The aim of this study was to investigate the feasibility of lung ultrasound in the diagnosis of neonatal respiratory distress syndrome (NRDS) in preterm infants. Methods One hundred and nine preterm infants were prospectively recruited. Three ultrasound diagnostic criteria were developed to diagnose preterm infants with NRDS: (A) thickened or not smooth pleural line, part of the lung field shows diffuse ‘B-line’ sign or alveolar-interstitial syndrome (AIS); (B) thickened or not smooth pleural line, all lung fields show AIS, signifying the ‘white lung’ sign; (C) thickened or rough pleural line, ‘white lung’ sign and ‘lung consolidation’ sign can be observed in any lung field. Results The sensitivity and negative predictive value of NRDS in preterm infants with diagnostic criteria A were 100%, but the specificity and positive predictive value were 67.95 and 55.36%, respectively. The specificity and positive predictive value of diagnostic criteria B and C were 100%, while the 95% CI of diagnostic criteria B was narrower than diagnostic criteria C. The sensitivity and negative predictive value of diagnostic criteria B were higher than that of diagnostic criteria C. Of the 31 NRDS cases, 15 cases had severe NRDS and the other 16 did not have severe NRDS. Conclusion Thickened or rough pleural line with white lung sign is an important characteristic for the diagnosis of NRDS by lung ultrasound. White lung sign combined with the lung consolidation sign had high diagnostic efficacy when distinguishing severe NRDS from not severe NRDS.