Abstract: Natural languages are consisted of alphabet set,word set,sentence set,paragraph set and essay set.More-over,alphabet set is included in word set；word set is included in sentence set；sentence set is included in paragraph set；paragraph set is included in essay set.In this way,natural languages are regular languages.As a specific example,English is consisted of English alphabet set,English word set,English sentence set,English paragraph set and English essay set.In this way,English is regular language.We also introduced ten concepts including English alphabet empty-graph,English alphabet empty-graph language,etc.Chinese is consisted of Chinese character set,Chinese word set,Chinese sentence set,Chinese paragraph set and Chinese essay set.In this way,Chinese is regular language.We also introduced ten concepts including Chinese character empty-graph,Chinese character empty-graph language,etc.These concepts and theories not only offer a new solution for natural language processing,but also establish a new research field for linguistics.

Key words: Natural language,English,Chinese,Regular language,Natural language processing,Essay set,English essay set,Chinese essay set,Essay digraph language,English essay digraph language,Chinese essay digraph language