Abstract: Objective To analyze the incidence and influencing factors of myasthenia gravis after thymectomy, in order to provide reference for clinical prevention of myasthenia gravis. Methods Ninety-two patients with thymectomy in our hospital from March 2019 to March 2020 were selected to observe and record the incidence of myasthenia gravis after operation. The patients were divided into group A and group B according to whether myasthenia gravis occurred after operation. The general data of the two groups were collected by questionnaire survey, the clinical data were sorted out, and the general data and clinical data of the two groups were compared. The risk factors of myasthenia gravis were analyzed by logistic regression analysis. Results There were 11 cases of myasthenia gravis(12.0%) after operation in 92 patients. The course of disease, combined immune disease, operation route, combined anterior mediastinal fat dissection, postoperative pulmonary infection, postoperative radiotherapy and chemotherapy were compared between the two groups, and the difference was statistically significant(all P<0.05). The results of multivariate logistic regression analysis showed that the course of disease(>12 months), combined immune disease, surgical route(open chest) and postoperative pulmonary infection were the risk factors of myasthenia gravis, and the combined anterior mediastinal fat dissection, postoperative radiotherapy and chemotherapy were the protective factors. Conclusion The incidence of myasthenia gravis after thymectomy is relatively high, and there are many influencing factors, such as long course of disease, combined with immune diseases, thoracotomy, postoperative pulmonary infection, etc. Therefore, we should take symptomatic treatment measures according to the risk factors of patients during thymectomy to reduce the incidence of myasthenia gravis and improve the effect of surgery.