About the Seon Master Hyegeo(慧炬), the National Preceptor during King Gwangjong(949~975), only a few things have been known. He had learned under the Fayan Master Wenyi(885~958) in China and trained the Seon Monks at Yeongguk-sa temple in Korea. A fragment of a stele for Hyegeo was found at the site of Yeongguk-sa temple in the foot of Mt. Dobong in Seoul in 2017 and it contains not a little important new information about his life and thought. In this paper we tried to examine his activities in China and Korea according to the stele-fragment, especially focusing on his philosophical lineage of Seon thought, in Korean and Chinese Seon[Chan] tradition. Hyegeo was born in Dongja village, the north west area of present Gimpo, became a monk when young. He studied the Seon thought in a monastery at Mt. Dobong under the disciple of Jeoljung, the real founder of Mt. Saja Seon Lineage in Korea, until around 933, when he went to China to learn more. In China, he learned under Fayan Wenyi and Yunmen Wenyan, the leading successors of Xuansha Shibei, whose Seon[Chan] thought was becoming the new influential trend in China at the time. He came back to Korea about 940 and tried to sprea the Xuansha and his disciples thoughts. He was regarded important and got the respect from the royal family during the middle of 10th century, when the disciples of Fayan Wenyi, who learned together with Hyegeo, became the leaders of Buddhism in Wuyue Kingdom, the most important diplomatic partner of Goryeo dynasty at the time. The influence of the Mt. Saja Seon Lineage and the Fayan Seon school became more important too. Hyegeo resided at Yeongguk-sa temple, the re-built monastery of Mt. Dobong and led the Goryeo Buddhism under the support of King Gwangjong until his death. Yeongguk-sa temple, one of the three Unchangeable Temples designated by King Gwangjong, must have been the center of Mt. Saja Seon Lineage and the Fayan Seon school at the time.