Abstract: In view of the possibility of a large potential earthquakes in the adjacent trenches along the southeastern coast of China, a numerical simulation of the M_w9.0 earthquake tsunami in both the Ryukyu Trench and Manila Trench is conducted using a shallow water numerical model GeoClaw based on the finite volume method.The results show that both the Ryukyu Trench and Manila Trench released tremendous energy at the time of the earthquake and spread to the coast of China in the form of tsunami waves.Among them, the tsunami triggered by the Ryukyu Trench earthquake reached the northern part of Fujian province three hours after it spread over the East China Sea continental shelf, and affected the coastal areas of Zhejiang, Shanghai and Jiangsu in the next two hours.The tsunami wave height generally reached above 0.5 m and local coasts of Zhejiang and Shanghai is above 1 m.The Manila trench earthquake and tsunami propagation process was smooth and reached the coast of Hainan two hours later, and in turn affected Zhanjiang, Macao, Hong Kong, Xiamen, Kaohsiung and other coastal areas.The wave height of tsunami generally reached above 2 m, and the coastal areas of Macao and Hong Kong reached more than 5 m, facing serious danger levels.Considering the continuous construction of offshore projects such as ports, nuclear power plants and drilling platforms in the southeast coast of China, it is necessary to study the potential tsunami threats and take corresponding measures.