Objective To investigate the clinical significance of changes in cardiopulmonary function, degree of hypoxia and inflammatory factors in obstructive sleep apnea hypopnea syndrome (OSAHS) patients combined chronic obstructive pulmonary disease (COPD). Methods A retrospective case-control study was conducted on 209 patients with OSAHS admitted from October 2015 to April 2022. The OSAHS patients were divided into an OSAHS-only group, an OSAHS combined with mild COPD group, an OSAHS combined with moderate COPD group, and an OSAHS combined with severe and very severe COPD group based on pulmonary function test. The characteristics of cardiopulmonary function [(pulmonary artery pressure, N terminal pro B type natriuretic peptide (NT-proBNP), forced expiratory volume in the first second to forced vital capacity (FEV1/FVC), percent predicted value of FEV1 (FEV1%pred)], hypoxia indexes [night lowest saturation of pulse oxygen (NL-SpO2), night medial saturation of pulse oxygen (NM-SpO2), saturation of pulse oxygen less than 85% of the time (TS85), diurnal lowest saturation of pulse oxygen (DL-SpO2)], inflammatory factor indicators [procalcitonin (PCT), interleukin-6 (IL-6), hypersensitive C-reactive protein (hs-CRP), neutrophil to lymphocyte ratio (NLR)], and other characteristics were compared separately. The partial correlation analysis and logistic regression were used to analyze the influencing factors of OSAHS with COPD. Results There were statistically significant differences in age, days of hospitalization, cardiopulmonary function indexes, hypoxia indexes and inflammatory factor indexes between the OSAHS combined with COPD group and the OSAHS-only group (all P<0.05). And pulmonary artery pressure, NT-proBNP, TS85, IL-6, and NLR were higher and DL-SpO2, NL-SpO2, and NM-SpO2 were lower in the OSAHS combined with severe and very severe COPD group compared with the OSAHS combined with mild COPD group (all P<0.05). In the partial correlation analysis, FEV1%pred was negatively correlated with pulmonary artery pressure, NT-proBNP, TS85, IL-6, hs-CRP and NLR, and positively correlated with DL-SpO2, NL-SpO2 and NM-SpO2 (all P<0.05). In regression analysis, NLR and TS85 were the main risk factors for OSAHS combined with COPD (all P<0.05). Conclusions OSAHS patients combined with COPD have longer hospital days, greater burden of hypoxia, cardiopulmonary function and inflammation compared with patients with OSAHS alone, especially more significant in patients with poorer pulmonary function, and higher incidence of pulmonary heart disease, atrial fibrillation, and lower limb edema. NLR and TS85 are the main risk factors in patients with OSAHS combined with severe and very severe COPD.