Objective：To explore the relationship between clinical characteristics and olfactory prognosis after the first endoscopic sinus surgery in patients with diffuse chronic rhinosinusitis with nasal polyps（CRSwNP）. Additionally，to establish and verify a nomogram prediction model for poor olfactory improvement after the first endoscopic sinus surgery in these patients. Methods：Clinical data were collected and analyzed from 67 patients with diffuse CRSwNP and olfactory dysfunction who underwent their first endoscopic sinus surgery at the Department of Otolaryngology，the First Affiliated Hospital of Nanjing Medical University. Based on the postoperative improvement in olfactory dysfunction，patients were categorized into an improvement group（50 cases）and a non - improvement group（17 cases）. Univariate and multivariate logistic analyses were conducted to identify factors influencing olfactory improvement. Based on these factors，a nomogram model was established and its predictive performance was evaluated. Results： Multivariate analysis indicated that the length of the disease course（β=0.527，OR=1.693，95%CI：1.139-2.517），Lund-Mackay sinus CT score（β=0.704，OR=2.021，95%CI：1.208-3.382），peripheral blood eosinophil ratio（β=0.311，OR=1.365，95%CI：1.026-1.815）， and the ratio of ethmoid to maxillary sinus CT scores（β=0.954，OR=2.597，95%CI：1.263-5.340）were independent predictive factors for diffuse CRSwNP patients with poor olfactory improvement after their first endoscopic surgery. The nomogram model constructed based on these factors showed an area under the receiver operating characteristic（ROC）curve is 0.770（95%CI：0.658-0.881，P ＜ 0.01），a C-index of 0.856（0.817-0.894），and a mean absolute error of 0.034 in the calibration curve. Conclusion：The nomogram model based on the disease course，Lund-Mackay sinus CT score，peripheral blood eosinophil ratio，and the ratio of ethmoid to maxillary sinus CT scores can predict olfactory improvement after the first endoscopic sinus surgery in diffuse CRSwNP patients，providing valuable clinical guidance.