Objective To investigate the clinical features and influencing factors of nasosinusitis caused by nasopharyngeal carcinoma (NPC) radiotherapy. Methods The clinical data of 228 NPC patients admitted to our hospital from January 2014 to June 2017 were retrospectively analyzed. According to whether the patients were treated with radiotherapy, the patients were divided into non-radiotherapy group (106 cases) and radiotherapy group (122 cases). The clinical characteristics of nasosinusitis were analyzed and compared. Univariate and multivariate logistic analysis was used to analyze the influencing factors of nasosinusitis after radiotherapy in patients with nasopharyngeal carcinoma. Results The incidence of sinusitis was 81.97% in the radiotherapy group, which was higher than that in the non-radiotherapy group (54.72%). The difference was statistical significance (P<0.05). The incidence of sinusitis involvement in the radiotherapy group was in the order of ethmoid sinus, sphenoid sinus, anterior ethmoid sinus, sinus ostium and nasal tract sinus complex, frontal sinus, and maxillary sinus. The incidences of ethmoid sinus and sphenoid sinus in the post-nasal sinusitis group were higher than that in the non-radiotherapy group (P<0.05). Univariate analysis showed that the occurrence of sinusitis after radiotherapy was related to whether the patient's age was > 50 years, whether the disease duration was >2 years, whether there was nasal invasion, tumor staging, whether nasal drops were used, and whether nasopharyngeal irrigation was performed. Multivariate logistic regression analysis showed that patients with a disease course of >2 years had nasal invasion and T3+T4 tumors were independent risk factors for sinusitis after NPC radiotherapy; use of nasal drops and nasopharyngeal washing were protective factors. Conclusion There is a higher incidence of sinusitis after radiotherapy of NPC, and mainly affects the ethmoid sinus and sphenoid sinus in the posterior group. Patients with a disease course of >2 years, with nasal invasion, and T3+T4 tumors should actively take measures to prevent the occurrence of sinusitis. The use of nose drops and nasopharyngeal washing is an effective measure to prevent the occurrence of sinusitis after NPC radiotherapy.