This paper is based on the view of ideology history to discuss the development of the thoughts of Japanese Tian-tai and the esoteric teaching. It embarks on an over view concerning the history of Japanese Tian-tai school and the founder of Tian-tai sect Zui-Cheng（最澄 767-822，Saicho in Japanese）, who gave the sutra and mantra teachings at same time. This paper mainly analyzes Japanese Tian-tai master Yuan-Jhen's new view point of Tiantai and the esoteric teaching, such as the teachings of mantra are higher than sutra, and establishing the "five teachings" system to supplement Tien-tai system of the "four teachings". The marked difference between Chinese and Japanese Tiantai schools is the combination of Tian-tai and the esoteric teaching in Japan. In the past, the two Chinese Tiantai masters Guang-Xiu and Wei-Juan do not deeply concern about the esoteric teaching. Their standpoints are based on Tiantai to systematize the esoteric teaching into doctrinal classification. But Yuan-Jhen tries to combine the esoteric teaching with Tian-tai as a rational system of doctrinal classification. Therefore he criticizes the Chinese Tiantai masters' wrong interpret of the esoteric teaching. Kong-Hai（空海，Kūkai, 774-835）, the Japanese mantrayana（真言宗，Shingon sect）founder, interprets other systems of doctrinal classification from the point of esoteric teaching. The standpoints, interpretation and points of view of these three masters are totally different. We conclude that the combination of Tian-tai and the esoteric teaching in Japan is based on the historic fact. In order to offer the inner rational explanatory for the facts, the masters created the unique view point of Japanese Tian-tai Pan-Jiao. Since the system of doctrinal classification is the production of times' interpretation demand, so it will be changed according to the different of time. Therefore, the works of the 21 centuries' system of doctrinal classification will keep going.
