In the Third year of Jōō (1654), Ingen Ryuki (1592-1673), a high monk of the late Ming and early Qing Dynasties in China, travelled to Japan. In the First year of Kanbun (1661), Obaku-san Mampuku-ji was built in Uji, Kyoto, and Obaku sect was founded in Japan. In the Sixth year of Kan'ei(1629), the 34-year-old Emperor Gomizunoo(1596-1680) abdicated and became a monk in May of the Fourth year of Kei'an (1651), entitled Yuanjing. The Emperor Gomizunoo had never met with Ingen in his whole life, but he became, on November 7th of the Seventh year of Kanbun (1667), successor to Ryokei Shosen (1602-1670), a disciple of the late Ingen, and inherited the religious doctrines of Obaku sect. Besides, Obaku-san Mampuku-ji held grand ceremony in memory of the Emperor Gomizunoo every year. This shows the profound relationship among the Emperor Gomizunoo, Ingen and Obaku sect. Previous researches on the relationship among the Emperor Gomizunoo, Ingen and Obaku sect were done mainly from the angle of history or religious beliefs. There are few investigations to be found on the reasons why the Emperor Gomizunoo converted to Ingen and Obaku sect. This paper, however, analyzes the Waka poems by the Emperor Gomizunoo and the letter Ingen wrote to him, and studies the connection between them in thoughts and feelings, so as to clarify the background for the conversion of the Emperor Gomizunoo to Ingen and Obaku sect. By analyzing the Waka poems by the Emperor Gomizunoo, we can see his profound Buddhist belief and his complete relief from the spiritual shacles after he converted to Buddhism. Ingen was over sixty when he travelled east to Japan. From his letter to the Emperor, it can be seen that the Zen of Ingen has reached the realm of freedom .This and the enlightenment of "letting go off body and mind" must have comforted the heart of the Emperor Gomizunoo to a great extent. In his letter, Ingen also sang praise of the dignity of the Emperor Gomizunoo, and thanked him for his help and protection. These sincere respects were also well conveyed to the Emperor Gomizunoo. Ingen was a learned and liberal minded high monk, quite open to the outside world, who was as inclusive as the Emperor Gomizunoo. It can be said that it was the resonance of these thoughts and feelings that provided opportunities for the Emperor Gomizunoo to seek further communication with Ingen.