Luhmann's social system theory can be widely applied in many disciplines whose subjects can be observed in the system.In the pragmatic and functional framework of text linguistics,the term “communicative field” is very similar to “social system” in the system theory;the text type belongs to the category of social system and it connects different subsystems of a society,functioning as a “structural coupling”;and the text functions—“area function”,“text function” and “effect function” are relevant to the environment,system and readers.This research opens up new horizons for the study of text pragmatics.