Background Adolescent idiopathic scoliosis (AIS) patients suffer from restrictive impairment of pulmonary function (PF) as a consequence of spinal and ribcage deformity. Statistic modelling of scoliotic geometry has been well-established based on low-dose biplanar X-ray device (EOS) imaging. However, the postoperative lung morphology change derived from EOS has not yet been studied adequately till now. Methods Twenty-five female AIS patients with severe right-sided major thoracic curve (aged 13–31 years; Cobb angle 45°–92°) underwent posterior spinal fusion (PSF) were prospectively recruited for standing EOS imaging at preoperative, postoperative, and 1-year follow-up (1Y-FU) stages. EOS-based lung morphology at frontal and lateral view was measured respectively to assess serial statistical changes in area and height. Results At frontal view, left lung area significantly increased postoperatively (104.7 vs. 125.1 cm2; P<0.001) but without continuous increase at 1Y-FU (125.1 vs. 124.5 cm2; P=0.084), whereas right lung area showed a slight but insignificant interval increase (median: 143.8, 146.5, 148.4 cm2 at preoperative, postoperative, 1Y-FU stage, respectively; all P>0.05). At lateral view, the increase in left lung area was slight without statistically difference (median: 175.8, 178.4, 182.5 cm2 at preoperative, postoperative, 1Y-FU stage, respectively; all P>0.05), while right lung area did not significantly change postoperatively (median: 209.9, 206.7, 212.4 cm2 at preoperative, postoperative, 1Y-FU stage, respectively; all P>0.05). At both frontal and lateral view, left lung height significantly improved at both postoperative and 1Y-FU stage (all P<0.05), while preoperative right lung height was not significantly different from postoperative and 1Y-FU value (all P>0.05). Conclusions EOS imaging demonstrates that left lung area in severe AIS may improve after PSF surgery. EOS may provide useful information about lung morphology change after PSF in severe AIS.