Abstract: In the period of “Qing Yuan Dang Jin” of Southern Song Dynasty, neo confucianist Zhu Xi was impeached and dismissed from office. In the meantime, his disciple, Cai Yuanding was imposed a heavy penalty and died in Daozhou because of demotion. On the causes of Cais death, many researchers believed that Cai was implicated just because of the powerful minister, Han Tuozhous inhibition on Zhu Xi, and he was totally innocent. But based on the scattered historical materials in the relevant period especially from the letters of Zhu Xi in the contemporary period, we can find that Cai was penalized severely partly due to the political background in that period but the hidden and direct cause was because of the event that Cai decided to relocate the Jianyang school to Huguosi because of the Geomantic Omen. This made the political opponents accuse Cai as an excuse and also because the event was related to Geomantic Omen, Zhu Xi and his descendants and disciples were all reluctant to reveal the truth behind it, which became the direct reasons of Cais death in Daozhou but the reasons were submerged.

Key words: Cai Yuanding, banishment, reason, Geomantic Dmen, Jianyang school