Taiping leshi 太平乐事 (Joy in the time of peace and prosperity) by Cao Yin 曹寅 (1658–1712), is a drama of uniqueness involving exotic subjects. Act 8, entitled The Joyous Japanese Songs, is about the King of Japan paying tribute to the Chinese emperor, and most parts of it are written in Chinese characters carrying only sounds. Cao Yin called the phonetic characters “Woyu” (the Japanese language). But what does this kind of unprecedented “Woyu” intend to convey and what is the historical background behind these “Woyu”? This paper attempts to interpret this drama based on Japanese scholarship on Chinese-Japanese vocabularies compiled in the Ming dynasty, and on research into Cao Yin’s knowledge about Japan through textual analysis.