There are three opinions about the dating of Ciyou Fa-1628, 1644 and 1704. The book has several editions and the opinion supporting 1628 was based on the fact that one edition has an introduction by ZHANG Jiebin who completed most of his pediatric books by 1628. But from the author' s preface and contents of the book, the author ought to be CHENG Yunpeng. So the opinion of "1628" is not reasonable. The other two opinions have differences of the understanding of the Jiashen year (a year's title in the sexagenary cycle of Heavenly stems and Earthly branches), which was mentioned in the author's preface.The Jiashen year of the Chongzhen emperor is 1644 but the Jiashen year of the Kangxi emperor is 1704. According to Huizhou Fuzhi, Shexian Zhi, Huangan Xianzhi and records about CHENG Yunpeng in the introduction (by ZHANG Xiliang and LI Lin) of Ciyou Fa, the book should have been completed in the Jiashen year of the Kangxi emperor, namely 1704.