Objective To explore the differences in lung function, neutrophil polarization, and serum total immunoglobulin E (IgE) levels among bronchial asthma patients, chronic obstructive pulmonary disease (COPD) patients, and asthma-COPD overlap syndrome (ACO) patients. Methods The retrospective analysis enrolled 127 patients with respiratory system diseases diagnosed and treated in Wuwei People’s Hospital between March 2016 and March 2019. Among them, 45 patients with moderate and severe bronchial asthma were in included the asthma group, 42 patients with acute exacerbations of COPD were included in the COPD group, and 40 patients with moderately persistent and severely persistent ACO were included in the ACO group. Forty-eight healthy examinees in the same period were selected as the control group. The pulmonary function [forced expiratory volume in one second (FEV1), forced vital capacity (FVC), FEV1 to FVC (FEV1/FVC) ratio, and percentage of FEV1 to predicted value (FEV1%pred)], neutrophil polarization, and serum total IgE levels of the four groups were compared. Results In the control group, the ACO group, the asthma group, and the COPD group, the FEV1 values were (3.65±0.79), (2.04±0.58), (1.81±0.46), and (1.59±0.43) L, respectively, the FVC values were (4.13±0.92), (3.18±0.76), (2.69±0.63), and (2.43±0.58) L, respectively, the serum total IgE levels were (92.36±12.20), (334.81±55.96), (455.61±65.59), and (142.65±28.36) U/mL, respectively, and the between-group differences were all statistically significant (P<0.05). In addition, the FEV1/FVC ratios in the asthma group, the COPD group, and the ACO group were (67.93±11.51)%, (63.81±9.22)%, and (61.28±9.23)%, respectively, the FEV1%pred levels were (74.55±11.70)%, (63.29±8.60)%, and (61.34±7.91)%, respectively, which were lower than those in the control group [(83.60±7.18)% and (94.23±8.21)%] (P<0.05). The spontaneous polarization rates in the ACO group, the asthma group, the COPD group, and the control group were (29.43±5.58)%, (25.11±4.09)%, (16.28±4.51)%, and (7.18±2.12)%, respectively, the arbitrary polarization rates in the ACO group, the asthma group, the control group, and the COPD group were (30.01±5.29)%, (25.76±5.53)%, (21.42±4.36)%, and (19.85±5.00)%, respectively, the directional polarization rates in the asthma group, the ACO group, the control group, and the COPD group were (14.67±2.30)%, (8.21±1.81)%, (5.12±1.10)%, and (2.52±0.63)%, respectively, and the between-group differences were all statistically significant (P<0.05). Conclusion There are certain differences in lung function, neutrophil polarization, and serum immunoglobulin E level among patients with bronchial asthma, COPD, and asthma-COPD overlap syndrome.