Korean scholar Shen Youzhen identified 187 pairs of Gujinzi(古今字) in the Chinese dictionary Diwuyou(≪第五游≫). These explanations are influenced by Chinese ancient exegetics, especially the traditional Chinese dictionaries such as Shuowenjiezi(≪說文解字≫) and Zhengzitong(≪正字通≫). Gujinzi explanation is one of the important stylistic rules in this book. It is an integral part of the explanation of each Chinese character. In addition to communicating the inter Chinese character relation, it also has other functions such as explaining the meaning of word, explaining the forming motivation of character, explaining the meaning of character component, building cross-reference rule, enrich the explanation, etc. Shen Youzhen’s concept of Gujinzi is the same as the understanding of ancient Chinese scholars, all referring to different writing styles of the same word in different time.