A large number of manuscripts of Venerable Master Hsu Yun (hereinafter referred to as ＂Hsu Yun＂), who is the research object of this paper, were destroyed in the ＂Yunmen Incident＂ in 1951. Therefore, this study explores Hsu Yun's twelve handwritten letters preserved and collected in the private library of Mr. Ceng, a lay Buddhist of Yilan, Taiwan. These precious letters answered Dharma questions raised by eight lay Buddhists including Yi Zun, Jian Quan, Guang Yuan, Hui Zheng, Yang Lu, Hua Ping, Li Hang and An Ci. This paper uses literature observation as the research method. It starts with understanding the identity of the aforementioned eight lay Buddhists and the date, the time sequence and the content of each ink written letter. Then, it compares these letters with the calligraphy of Hsu Yun collected in the same library to verify their authenticity based on the style, format, date and using of seals. Furthermore, it traces the eight lay Buddhists' Dharma practice back to Hsu Yun and examines their thought relationship. From the contents of two letters between Elder Master Hsu Yun and An Tse, we can understand Hsuan Hua inherited the practice and thoughts from Elder Master Hsu Yun. They both undertook Three-Steps-One-Bow pilgrimages for filial piety, insisted on abiding by the precepts and living an ascetic life, advocated ＂Every Dharma is Equal＂, and propagated five Buddhist sects which are Chan, Pure Land, Vajrayāna, Vinaya and Teaching. In addition, they both focused on practicing and promoting Chan Buddhism, obtained spiritual powers knowing the past and the future, administered famous temples, and were adept at building forest monasteries to cultivate disciples and promote Buddhism. Hsuan Hua was finally affirmed by Elder Master Hsu Yun, who transmitted the Guiyang lineage of Chan Buddhism to him and made him the forty-sixth generation since Sakyamuni Buddha, the ninth lineage holder of the Guiyang school of Chan Buddhism. Thus, he became one of the ten great disciples of Elder Master Hsu Yun. It can be seen that before the advent of information technology, handwritten letters could achieve the function of propagating the doctrine and resolving doubts.
