Guhuan (顧歡)'s Yixialun (夷夏論) is one of the most important documents in the medieval intellectual history, also in the religious history of China. This paper argues that Guhuan’s radical attitude to Buddhism was correlated to the situation that Buddhism was overwhelming Taoism in Kuaiji region since the 5(superscript th) century through the description of the religious development in Kuaiji (會稽) region where Guhuan lived and the particular time when Yixialun was written out. Furthermore Yixialun was written in the same time when Luxiujing (陸修靜) came to Jiankang (建康), the aim of this document is not only to repel Buddhism directly, but also to criticize the taoists who want to tolerate Buddhism.