This article`s object of study is Situga(蛭牙) who is one of the characters in "Sango Shiiki"(三敎指歸)of Kuukai(空海) and is put in the panorama of the works of Kuukai(空海) in order to understand the character`s image, effect and nature. Besides in "Sango Shiiki"(三敎指歸), you can also see this character in the other works of Kuukai(空海). Therefore, this article will do research on his other works -- "Shoryoshu"(性靈集),"Jujushinron"(十住心論) with the purpose of better understanding the characteristics of his image and effect. The results of my research are as follows: Firstly, the reason why I set this character is the debate among Confucianism, Buddhism and Taoism in Japan at that period. In order to deal with his own insights into the three religions, Kuukai(空海)used his nephew as a model, commonly educated by the three religions. Therefore, that figure was the starting point of Kuukai(空海)`s literature. Secondly, in the addition to "Sango Shiiki"(三敎指歸), you can also find it in "Shoryoshu"(性靈集).The comparison to animals used in the two works is not to look down upon such people as Situga(蛭牙), but to influence and educate them, which is originated from Kuukai(空海)`s Buddhist merciful desire. So this figure also reflects his starting point of his thoughts of Esoteric Buddhism. Thirdly, with the help of this character, Kuukai(空海)can show his attitude to the debate of three religions and began spreading Buddhism from then on. As a monk sent to Tang, he learned authentic Esoteric Buddhism in Changan of the Tang Dynasty, which was brought back to Japan, and started to save all beings. After the "Shoryoshu"(性靈集) and other works, Kuukai(空海)`s thought ,dating from the setting of Situga(蛭牙), gradually became mature in the practice of all beings and finally formed the "Jujushinron"(十住心論). Situga (蛭牙) `s heart is the first heart of "Jujushinron"(十住心論)of the butting goat`s heart, which is the theoretical base on "Jujushinron"(十住心論). Consequently, Situga(蛭牙)`s real image and characteristic is made clear.