Objective: To explore the relationship between the clinical characteristics of patients with diffuse chronic rhinosinusitis with nasal polyps (CRSwNP) and olfactory outcomes after endoscopic surgery, and to establish and verify a nomogram predictive model for poor olfactory improvement in diffuse CRSwNP patients post-surgery. Methods: 67 diffuse CRSwNP patients with olfactory dysfunction who underwent their first endoscopic sinus surgery at the Department of Otolaryngology of the First Affiliated Hospital of Nanjing Medical University, were prospectively collected and analyzed for clinical data. Based on the postoperative improvement in olfactory dysfunction, patients were categorized into olfactory improvement group and no improvement group. Factors influencing olfactory improvement were identified through univariate and multivariate logistic analyses. A prognostic nomogram model for predicting postoperative olfactory outcomes in diffuse CRSwNP patients was then established and assessed to predict its accuracy. Results: The study included 67 diffuse CRSwNP patients with olfactory dysfunction， 50 of them showed improvement in their sense of smell, while 17 of them did not exhibit improvement. Multivariate analysis indicated that disease duration (β=0.527, OR=1.693, CI: 1.1392.517), Lund-Mackay sinus CT score (β=0.704, OR=2.021, CI: 1.2083.382), peripheral blood eosinophil percentage (β=0.311, OR=1.365, CI: 1.0261.815), and the ratio of ethmoid sinus to maxillary sinus CT scores (β=0.954, OR=2.597, CI: 1.2635.340) are independent predictive factors for diffuse CRSwNP patients with poor olfactory improvement after their first endoscopic surgery. The nomogram model for improvement in olfaction in patients with diffuse CRSwNP after initial endoscopic surgery was constructed based on these factors. The area under the receiver operating characteristic curve(ROC)is 0.770 (95% CI: 0.658~0.881, P<0.01), the C-index is 0.856 (0.817~0.894), and the average absolute error of the calibration curve is 0.034. Conclusion: We constructed a nomogram model to predict the olfactory improvement in patients with diffuse CRSwNP after their first endoscopic surgery based on disease duration, Lund-Mackay sinus CT score, peripheral blood eosinophil percentage, and the ratio of ethmoid sinus to maxillary sinus CT scores, offering a meaningful guidance for clinical practice.