1) rhymes and rhymes. He thinks that the rhyme and anti-rhyme in Guang Yun are the reflection of the rhyme-cutting system. In fact, the rhymes and rhymes he used are the guide to smooth and cut rhymes in the front of Kangxi Dictionary.

2) Chinese dialect, he used his field investigation data in Shanxi, Shaanxi, Gansu, Henan and other places, as well as dialect dictionaries in Guangzhou, Hakka and Fuzhou;

3) Foreign language loanwords are mainly used in Japanese translation of Wu Yin (5th-6th century), Japanese translation of Chinese Yin (6th-7th century), Korean loanwords (about 600 AD) and Vietnamese loanwords (9 9- 10/0th century).

Based on these materials, Gao Benhan determined the phonological category of medieval Chinese by association method, that is, according to the words cut back, and according to the words cut back.

Gao Benhan established the important position of association method from the perspective of methodology, making it a classic method to extract and analyze phonology in philology. Based on this method, the phonological framework of Middle Ages phonology (rhyming phonology) was established. Taking this as the construction object, Gao Benhan compared the pronunciations of more than 30 domestic dialect points with the phonological values of several foreign dialects, and comprehensively constructed the initial and final system of Middle Ages, in which a typical historical comparison method was adopted.

It can be seen that in this book, Gao Benhan adopted the method of combining philology with historical comparison. This combination is a progress in methodology, and the two methods have their own application fields, each revealing an aspect of ancient sound. But fundamentally speaking, Gao Benhan's textual research method of ancient sounds is mainly philology, supplemented by historical comparison.

However, it is this complementary historical comparison method that brings a brand-new atmosphere to the study of China's phonology and leads it to a broad field. In this book, dialects and loanwords played a very important role in the reconstruction of medieval phonology. For example, according to the independence of the second-class food rhyme in Guangzhou dialect, its position in phonology is established; According to the separation of pronunciation in Vietnamese loanwords, the third and fourth languages are separated.

1. This layer is necessary to construct China ancient sound and make it the starting point of systematic modern dialect research;

2. Make a complete description of the pronunciation of Chinese dialects, and just pass this layer;

3. Use phonological research to explain how modern dialects evolved from ancient sounds.

Gao Benhan's study of China's phonology laid a solid foundation for completing this grand blueprint. Later, after textual research and correction by Fang Guili, Luo Changpei, Wang Li, Dong Tonghe, Li Rong and others, some omissions in the study of Gao were improved and corrected, which made the study of Chinese phonetic history perfect day by day.