Objective To explore the therapeutic effect of nasal cavity volume expansion surgery combined with modified uvulopalatopharyngoplasty （UPPP） on patients with obstructive sleep apnea-hypopnea syndrome （OSAHS） complicated by multi-level obstruction. Methods A total of 98 patients with moderate-to-severe OSAHS， whose obstructive levels were located in the nasal cavity and pharyngeal cavity and who received treatment in our hospital from August 2023 to May 2025， were selected as the research objects. They were divided into two groups using the random number table method， with 49 cases in the control group and 49 cases in the observation group. The control group was treated with UPPP， whereas the observation group was treated with nasal cavity volume expansion surgery on the basis of the treatment for the control group. Two months after surgery， the clinical efficacy of the two groups was evaluated. Before and after treatment， the apnea-hypopnea index （AHI）， arousal index （AI）， lowest pulse oxygen saturation （LSaO₂）， Epworth Sleepiness Scale （ESS） score， Mini-Mental State Examination （MMSE） score， and PSQI score of patients in the two groups were compared. Pulmonary function before and after treatment was evaluated by FEV1 and PEF. Meanwhile， the occurrence of postoperative complications was recorded. Results The observation group exhibited a significantly higher total treatment efficacy rate than the control group （89.80% vs. 71.43%， P < 0.05）. The Apnea - Hypopnea Index （AHI）， Arousal Index （AI）， Epworth Sleepiness Scale （ESS） score， and Pittsburgh Sleep Quality Index （PSQI） score in the observation group were （10.26 ± 2.48） times/hour， （11.48 ± 3.08） times， （5.04 ± 1.08） points， and （6.89 ± 1.56） points， respectively， all of which were lower than those in the control group. Meanwhile， there were significant differences in the LSaO?， cognitive function， and pulmonary function between the two groups （P < 0.05）. In terms of adverse reactions after treatment， there were 3 cases of cough and 1 case of suffocation in the observation group； in the control group， there were 2 cases of cough， 2 cases of suffocation， 2 cases of bleeding， and 1 case of dysphagia. There was no significant difference in the incidence of adverse reactions between the two groups （P > 0.05）. Conclusion The combination of nasal cavity volume expansion surgery and UPPP can improve the clinical efficacy for OSAHS patients with multi-level obstruction， enhance their cognitive function and sleep quality， and does not increase the risk of adverse reactions.