Abstract: During the Ming and Qing dynasties， there were frequent exchanges between China and Ryukyu. As an official channel established by China， the Chinese envoys crossed the East China Sea dozens of times and exchanged with each other. The natural environment of the ChinaRyukyu sea route is complicated. And the travel of the envoys had not only the danger of piracy， but also the danger of rough seas and broken ships. In order to cope with the risks caused by the natural forces during the voyage， the Chinese envoys took preventive measures such as improving the performance of the boat， improving navigation techniques， selecting talents and storing emergency supplies. While ensuring the safety of the voyages， these preventive measures also had a positive impact on the shipbuilding， and navigation technology， culture， and agriculture of Ryukyu， and promoted the development of the vassal relationship between China and Ryukyu.

Key words: envoy ships； seamanship； prevention strategy； ChinaRyukyu relations