Abstract: Language choice is the focus of theoretical linguistics and applied linguistics. Language choice refers to the way in which the user constructs words and sentences, within psychological and grammatical norms of “conventions” to express meaning and doing things. Based on the theory of sociolinguistics, pragmatics and systemic-functional linguistics about the interaction among language, user and society, the paper first argues that language choice is related to the selective use and social transmission of alternative languages and variants, and is characterized by communicative, contextual and conventional characteristics. Secondly, language choice has the social functions of expressing ideas and taking effect by words. By choosing different languages or words to conform to the normative meaning, discourse meaning is generated to realize the functions of expression and effectiveness.