Written during the reign of King Sukjong of the Joseon Dynasty, Yeyi Language Jiejie is the earliest existing book of Yeyi Language Jiejie, and it is also a modern Chinese textbook. It contains rich words in modern Chinese. The book classifies the words in categories such as astronomy, season and climate, and uses Korean translation and phonetic transcription to complement textbooks in various languages. The 17th and 18th centuries were the period with the highest frequency of epidemic diseases in China. There are 94 “diseases” words in the book. By analyzing the specific symptoms of “diseases” words, these words are reclassified into 10 categories. Such as “clinical symptoms” category, “infectious diseases” category, “neurological diseases” category, “metabolic diseases” category, “venereal diseases” category, “parasites” category, “acute” category, “surgical diseases” category and others. It is found that the changes of “disease” are relatively conservative, and most of the words are still in use in modern Chinese. In addition, there are 34 dissimilar words in the category of “disease”. According to the changes of the font components of the 34 dissimilar words, this paper divides them into 11 types, such as: brushsaving change, same deformation of strokes, same replacement of strokes, brushsaving replacement, additional replacement, additional stroke, saving stroke, reducing stroke, replacement and deformation.