本文在阐明“字音类”和音类关系的基础上,重点讨论古字音类今读分合在汉语方言历史比较中的依据、内容、方法和意义。文章提出古字音类变化率和古字音类今读合并率这两个适用于汉语方言字音类历史比较新概念:前者适合做单个方言古今字音类的比较,后者适用于跨方言字音类的比较。 On the basis of clarifying the relation between phonetic class and phonetic class, this paper focuses on the basis, content, method and significance of ancient phonetics classics in the historical comparison of Chinese dialects. The article proposes that the rate of change of ancient phonetic characters and the present rate of ancient phonetic transcription combined rate are relatively new concepts applicable to phonetic class history of Chinese dialects: the former is suitable for the comparison of ancient phonetic phonetic class of single dialect, and the latter is suitable for the comparison of cross-dialect phonetic class .