Objective To investigate the efficacy of vitamin D (VD) as an adjuvant therapy for chronic sinusitis with nasal polyps (CRSw NP) and its effect on serum inflammatory factor levels. Method: 96 patients with CRSw NP admitted to the First Affiliated Hospital of Nanyang Medical College from January 2021 to April 2024 were randomly divided into a control group and a study group, with 48 patients in each group. The control group was treated with budesonide nasal spray combined with endoscopic sinus surgery (FESS), while the study group was treated with VD oral adjuvant budesonide nasal spray combined with FESS surgery. Both groups received medication for 8 weeks. After the completion of treatment, efficacy evaluation was conducted to compare the inflammatory factors [interleukin-4 (IL), IL-6, tumor necrosis factor (TNF) - α], nasal mucosal structure (Lund Mackey and Lund Kennedy scores), and nasal ventilation function [nasal volume (NCV), minimum cross-sectional area of nasal cavity (NMCA), and distance from minimum cross-sectional area of nasal cavity to anterior nostril (DCAN)] before and after treatment. After the end of treatment, the total effective rate of the study group was 93.75% (45/48), which was higher than the control group's 77.08% (37/48) (P<0.05). After treatment, IL-4, IL-6, TNF - α, Lund Mackey score, Lund Kennedy score, and DCAN in both groups of patients decreased significantly compared to before treatment, and the levels in the study group were lower than those in the control group (P<0.05). NMCA and NCV in both groups of patients increased significantly after treatment, and the levels in the study group were higher than those in the control group (P<0.05). Conclusion: VD assisted budesonide nasal spray combined with FESS is effective in treating CRSw NP, and is beneficial for improving postoperative inflammatory factors, nasal mucosal structure, and nasal ventilation function.