Objective:To investigate the efficacy of functional endoscopic sinus surgery（FESS） in the treatment of olfactory dysfunction in patients with chronic rhinosinusitis with nasal polyps （CRSwNP） , at the same time, it provides an evidence for the prognosis evaluation of olfaction and the clinical application of oERPs to evaluate the plasticity of olfaction cortex. Methods:From October 2021 to October 2022, 45 patients with CRSwNP who underwent FESS nine-step standardized treatment in our department were recruited as the research subjects, divided into 22 patients with eosinophilic CRSwNP（ECRS）and 23 patients with non-eosinophilic CRSwNP（nECRS）. VAS-olfactory dysfunction （VAS-OD） score, SNOT-22 olfactory score, Sniffin' Sticks test and oERPs collection and processing were performed before the operation. All items were evaluated again 3 months after the operation. Results:VAS-OD and SNOT-22 olfactory score were significantly lower in all CRSwNP patients after the operation than those before the operation[F（1, 43） =357.429, P<0.001; F（1, 43） =185.657, P<0.001], the scores of T, D, I and TDI scores in Sniffin' Sticks test were significantly higher than those before the operation[F（1, 43） =126.302, P<0.001; F（1, 43） =311.301, P<0.001; F（1, 43） =131.401, P<0.001; F（1, 43） =295.885, P<0.001]; The decrease of VAS-OD and SNOT-22 olfactory score in the ECRS group was smaller than that in the nECRS group[F（1, 43） =4.825, P=0.033; F（1, 43） =9.916, P=0.003], T, D and TDI scores were significantly lower in nECRS group than those in nECRS group[F（1, 43） =6.719, P=0.013; F（1, 43） =4.890, P=0.032; F（1, 43） =4.469, P=0.040]; There was a positive correlation between preoperative eosinophil-to-lymphocyte ratio（ELR） and SNOT-22 olfactory score and how much it changes（r=0.455, P=0.002; r=-0.414, P=0.005）, a negative correlation between T, TDI score and how much they change respectively（r=-0.431, P=0.003; r=-0.385, P=0.009; r=-0.383, P=0.010; r=-0.316, P=0.035）. The latency of P3 was significantly shorter after operation than that before operation in all CRSwNP patients[F（1, 14） =24.840, P<0.001], however, the amplitude has no significant surgical effect. Conclusion:FESS could significantly improve the olfactory function of CRSwNP patients, while changes in plasticity may occur in the olfactory cortex. In addition, the preoperative peripheral blood eosinophil granulocyte level can predict the postoperative olfactory improvement.