“Differentiation of form” plays an important role in Tang Lan’s theory system. It is not only an important path to the evolution of characters, but also the theoretical basis of the natural classification created by Tang Lan. This theory is put forward in the second part of ‘The Origin and Evolution of Writing’ and in the Fourth quarter of ‘Composition of Ancient Chinese Characters’, in Introduction to Ancient Philology. According to Tang’s theory, the earliest text is hieroglyphs, but some rarely recorded real name is not representative of hieroglyphic language. In order to record language, hieroglyphics produced three kinds of methods: shaping evolution under the guise of differentiation, meaning extension, and transliteration. ‘Six Skills’ in Chinese Philology section of the “differentiation” is very different to Introduction to Ancient Philology, only one point is probably the same (i.e. change form). The differentiation in China Philology, including corruption and division, also touched the variant that includes differentiation, differentiation due to evolution caused by the text, these are not involved in Introduction to Ancient Philology. This paper makes a detailed analysis of Tang’s differentiation examples on different occasions, so as to understand his theory more accurately and to explore the theoretical value of his theory of “form differentiation”.