Abstract: Objective　To discuss the pulmonary function change in infants with human bocavirus (HBoV) pneumonia or mycoplasma pneumonia (MP) and its clinical significance. Methods One hundred and forty infants under 3 years old who were admitted due to pulmonary infection were recruited from January, 2013 to October, 2013. Among them, HBoV-DNA was detected in 64 cases, and MP-DNA was detected in 76 cases. Thirty eight normal age-matched infants were selected as controls. The shape of tidal breathing flow-volume loops (TBFVLs) and change of every index were measured with a Pulmonary Testing System (Jaeger MasterScope). Results The ratio of time to peak tidal expiratory flow (PTEF) to total expiratory time (TPTEF/TE), the ratio of VPTEF to expiratory volume (VPTEF/VE), tidal expiratory flow at 25% of the remaining tidal volume (TEF25%) and the ratio of TEF25% to PTEF (25/PF) were significantly decreased in infants with HBoV and MP infection as compared with healthy infants (P<0.05). However, there was no significant difference of the above indices between infants with HBoV and MP infection (P>0.05). The shape of TBFVLs in infants with HBoV and MP pneumonia was changed and characterized by left-shifted PTEF and trough-like concave in descending limb. The PTEF was decreased in infants with pulmonary infection. Conclusions HBoV or MP infection results in impaired pulmonary function with manifestations of obstruction in small airway. The shape of TBFVLs in infants with HBoV and MP pneumonia is characterized by left-shifted PTEF and trough-like concave in descending limb.