Purpose: To investigate the efficacy of N-acetylcysteine as an adjuvant therapy in chronic obstructive pulmonary disease (COPD) with pulmonary interstitial fibrosis (PIF), and its effect on inflammatory factors and serum vascular endothelial growth factor (VEGF) levels. Methods: A total of 94 patients with COPD-PIF from May 2020 to May 2022 in Wuhan Fourth Hospital, China were equally randomized into study and control groups. Control group was administered conventional treatment while the study group was given N-acetylcysteine in addition to conventional treatment. Therapeutic efficacy, forced expiratory volume in the first second (FEV1), forced vital capacity (FVC), FEV1/FVC, blood gas, pulmonary fibrosis, and oxidative stress were evaluated. Changes in inflammatory factors, serum vascular endothelial growth factor (VEGF), and incidence of adverse drug reactions were compared. Results: The study group showed significantly higher efficacy, FEV1, FVC, FEV1/FVC compared to control group (p < 0.05). Also, study group showed significantly higher partial pressure of oxygen (PaO2), blood oxygen saturation, superoxide dismutase (SOD), and glutathione (GSH) levels after treatment compared to control group (p < 0.05). Platelet-derived growth factor (PDGF), transforming growth factor (TGF-β), vascular cell adhesion molecule (VCAM), tumor necrosis factor (TNF), interleukin-6 (IL-6), and vascular endothelial growth factor (VEGF) levels after treatment were significantly lower in the study group than in the control group (p < 0.05). Conclusion: N-acetylcysteine as an adjuvant therapy for COPD-IF is highly effective, improves lung function and oxidative stress, reduces airway inflammation, and VEGF, and attenuates the degree of hypoxia and pulmonary fibrosis with no serious adverse effects. A larger sample size, multicenter, randomized trials to validate these findings and evaluate the downstream regulatory mechanism of Nacetylcysteine in COPD-PIF.