Variant characters in literature is a kind of valuable material for the study of the history of the Chinese language, contrasting and emending variant characters is also an important method. Nevertheless, as variant characters in the literature are complicated, we should be particularly cautious with it, otherwise, it is easy to misjudge and misunderstand, so as to misuse the variant characters as arguments in the research and even arrive at a wrong conclusion. Combined with specific research results, this paper discuss the following three problems which should be noticed when using Variant Characters in the study of the history of the Chinese Language: distinguishing the nature of the variant characters, distinguishing the authenticity of the variant characters, and distinguishing the source of the variant characters. The nature of variant characters caused by different reasons is also diverse, generally speaking, which can be divided into three types: collational variant characters, scripting variant characters, and rhetorical variant characters. Processing methods and research values for different variant characters with diverse nature are also different. For the collational variant characters, we should use the methods and principles of literature sorting to distinguish; Theory and method of philology should be applied to scripting variant characters to identify the relationship between different scripts; Theories and methods of linguistics (history of Chinese Language) should be applied to rhetorical variant characters to explore the alternative relationship between words and between sentences. When taking advantage of variant characters in the study of the history of the Chinese Language, we must recognize the nature of variant characters, once confused by variant characters with different nature and choose improper methods to research, then we wouldn't get the truth. Using variant characters (scripting variant characters and rhetorical variant characters) as materials for the study of the history of the Chinese Language, the methodology involved is comparison; But effective comparison should be based on the authenticity of comparison items. With the circulation of texts，one of the Variant characters ″A—B″ could get wrong (such as A becomes A'), then it seems right that the variant characters ″A—B″ became ″A'—B″. However there is not true correspondence between A' and B. Actually, authentic comparison item for B is not A' but A. This situation will confuse researchers and bring trouble to research, so attention must be paid to the authenticity of comparison items when using variant characters to establish the validity of arguments. Great progress has been made with regard to make language comparison using rhetorical variant characters to explore the development of Chinese lexical grammar and style transformation. However, working on such comparative research, must confirm the authentic source of variant characters. Only by establishing a true correspondence between variant characters can we effectively compare and avoid the disadvantages of aimlessness.