Objective：To investigate normal values of tidal breathing parameters in infant at different gestational ages without respira－tory complications and to analyze their differences. Methods：Totally 25 preterm infants less than 34 gestational weeks，30 late preterm infants and 55 healthy full term infants were studied on 1，14，28 d after birth. Tidal breathing parameters were measured by ultrason－ic flow meter. Results：Values of tidal breathing parameters were normally distributed. Ratio of time to peak expiratory flow/expiratory time，ratio of volume to peak expiratory flow/expiratory volume，tidal expiratory flow at 75% remaining tidal volume（TEF75），tidal expi－ratory flow at 50% remaining tidal volume（TEF50），tidal expiratory flow at 25% remaining tidal volume（TEF25） were gradually in－creased on 1，14，28 d after birth in three groups，but respiratory rate（RR） was gradually decreased. Prominence correlation of RR and TEF75，TEF25 was found in full term infants（r=0.469，P<0.01；r=539，P<0.01）；correlation of RR and TEF25（r=0.231，P<0.05） and correlation of RR and TEF75（r=0.130，P >0.05） were found in late preterm infants. There was no correlation of RR and TEF25，TEF75 in preterm infants born less than 34 gestational weeks（r=0.190，P >0.05；r=0.220，P >0.05）. At a matched post men－strual age of 40 weeks，preterm group had lower TEF25，TEF75，TEF25 and tidal volume per kilogram，higher RR compared with those in full term group（P<0.05）；there were no difference in above parameters between late preterm group and full term group（P >0.05）. Conclusions：Lung function of infants in the three groups is improved with the increase of gestational days. At the corrected ges－tational age 40 weeks，preterm infants less than 34 weeks fail to achieve catch-up growth in tidal breath parameters. Correlation of RR and TEF75，TEF25 is found in full term infants not in preterm infants. Infant lung function tests and correlation analysis are very im－portant ways to assess lung development，especially for preterm infant. Tidal breathing parameters in infants at different gestational ages could be used as clinical references.