Objective To compare the different surgical treatment methods of thymoma combined with myasthenia gravis (MG), and to discuss the clinical effectiveness of thoracoscopic combined mediastinoscopic extended thymectomy. Methods We retrospectively analyzed the clinical data of 58 patients of thymoma combined with myasthenia gravis in Northern Jiangsu People's Hospital between 2011 and 2016 year. According to the operation method, the patients were divided into three groups including a group A for thoracoscopic thymectomy (n=32), a group B for thoracoscopic combined mediastinoscopic thymectomy (n=15), and a group C for transsternal thymectomy (n=11). The clinical effects were observed and compared. Results In the group A and the group B, the bleeding volume, postoperative hospital stay and other complications were significantly lower than those in the group C with statistical differences (P<0.05). The incidence of myasthenic crisis in the group B (6.7%) was less than that in the group C (36.4 %), but the difference was not statistically different (P=0.058). The operation time of the three groups was 122.0 ± 39.4 min, 130.3 ± 42.5 min, and 142.3 ± 40.8 min respectively with no statistical difference between the two groups (P>0.05). The rate of dissection grade in the group B (grade 1, 12 patients, 80%) was significantly greater than that in the group A (grade 1, 14 patients, 43.8%,P<0.05). The effective rate of the group A, the group B, the group C was 84.4%, 93.3% and 90.9%, respectively with no statistical difference between groups (P>0.05). Conclusion The thoracoscopy combined mediastinoscopic thymectomy not only has the advantages of less trauma, quicker recovery and fewer complications, but also can more thoroughly clean the thymus and adipose tissue, which can achieve the same therapeutic effect as the transsternal thymectomy.