The Chinese characters distinguish from one another by their forms. The transmission of information and social communication are possible only when generally recognized forms of the characters are used, written and read. This paper deals mainly with the different forms of characters between ancient literature and modern usage of the characters, which may cause confusion. For the convenience of expression, all the characters that are identical both in ancient and modem time are referred to as "regular Chinese characters" and all the characters that are different in forms are called "variant Chinese characters."Some of the variant Chinese characters used in ancient times were variants of the regular characters; some were the regular characters at the time but later became non-standardized (like the difference between ancient and modern characters and between the traditional and simplified Chinese characters). To read the characters correctly, modern readers have to convert the words and phrases written with the variant characters into their corresponding regular characters.The significance of the study of the "variant Chinese characters" lies in the following points. 1. It guides reading and sorting out of ancient medical classics, enables researchers and readers to understand them correctly and aids in the general study of the ancient literature; 2. It enables us to explore into the relationship between ancient Chinese characters and words and the regularities of phrase understanding so as to enrich the study of the history of the Chinese language; 3. It enables us to supplement and revise large-sized Chinese reference books and accumulate basic materials for compiling professional dictionaries; 4. It enables us to clarify the sources of the words and phrases so as to facilitate data processing on the computer; and 5. It enables us to rearrange and recompose theories on ancient Chinese language so as to assist its research and teaching.This study consists of two parts. The first part is the macroscopic and theoretical exploration of "variant Chinese characters" and the overall analysis of the mechanism of formation and variation types of "variant Chinese characters," with theoretical ingenuity. The second part is the microcosmic analysis of concrete cases of "variant Chinese characters" based on the theoretical studies, and many problems have been solved, which confirmed the validity of the theoretical studies.As the appendix, "Translation of Variant Chinese Characters in Ancient Classics on Traditional Chinese Medicine" is written, which is divided into groups (each group containing one regular Chinese character and several corresponding variant Chinese characters) and aims to explain and analyze the changes of some of the typical "variant Chinese characters." Under the entry of one regular Chinese character, as many corresponding variant Chinese characters as possible are collected so as to reflect an overall picture of the various forms of a certain word in ancient classics on traditional Chinese medicine.