The purpose of the study aim to analyze the activities and achievements of buddhist priests in China in the period of late Koryo dynasty . But limits of these documents were so distinctive that the understanding about true history of them were very difficult. Fortunately, records concerning them could be found on China's documents, which supports existence of them. In this study I had tried to illuminate their life in China and seeking after historical truth of buddhism. Definitely, this study aim to explain activities and achievements of the main branch of Buddhism in China in the period of late Koryo dynasty. Firstly, Yuga'ca'ra(瑜伽宗)'s priests didn't flourished during the millitary government-period of Koryo dynasty and had shared some of basic features of chinese buddhism. But at the situation of chinese Budddhism under the dominaion of the Yu'an(元) dynasty, following reqests by the mongol court, many Buddhist monks were sent to the capital Tadu(大都) in order to copy entire sets the Sutras, in which priests of Koryo dynasty particularly had well versed. Taking this opportunity ,two Yuga'ca'ra's priests became national Preceptor(國尊) during the period of mongol influence by the controll of the religion affairs of the whole country. For example, the high priest of Yuga'ca'ra appointed Hyeyoung(惠 永), Meesoo(彌授) as national Preceptor(國尊) and Hyewon(海圓) acted as high priest in mongol empire. Secondly, Hua-yen school(華嚴宗)'s priests also didn't flourished during the millitary government-period and shared some of basic features of chinese buddhism. I investigated Hua-yen school Priest(華嚴宗僧侶), for example, Cheonhee(千熙), Wooun(友雲) as well as Dalhwan(達幻), Jeongjo(晶照), Joongjo(中向), Yarhan(若蘭), Hyewol(慧月) etc. who had acted in China under the domination of Y‘an dynasty. they were gone to China and seeked truth of Budddhism or took some of buddhist services. Cheonhee(千熙) studied in China under the domination of Y‘an dynasty for two years. He was recommended Chunhee (千熙) who belonged to Hua-yen school buddhist sect(華嚴宗) as national Preceptor(國師). He accepted reverence from chinese buddhists when he went to China(the Y'an Dynasty). In the same manner, Chunhee(千熙) had to purify the religious buddhism. After he was appointed to Hua-yen school(華嚴宗) as national Preceptor(國師), Wooun(友雲) studied also in China at that time. they decided to reform their buddhist doctrines which is needed for new times. Thirdly, the T'ien-t'ai School(天台宗)'s priests were unfolded buddhist movement of Baekryen-temple(白蓮社) during the millitary government-period(武臣執權期). Cheonchaek(天頙) were interchanged between Koryo Buddhist and china Buddhist. Under the regime of Y‘an dynasty, King Chungryol(忠烈王) founded Myoryensa(妙蓮寺) in Gaekyong(開京), he appointed Baekryeonsa's priests into Myoryensa's master priests. Euisun(義璇), who was one of the relative priests of famous aristocrat clan Cho-ingyu(趙仁規), changed Baekryonsa's traditional, buddhist and philosophical spirit to aristocrat-oriented buddhism. This trend appeared in Heeam(熙菴) and he studied also in China. And Dalmok(達牧) was established buddhist service in China. It was interpreted that they wanted the renovation of Buddhism in the period of late Koryo dynasty.
