Apart from studying overt types in language,Systemic Functional Grammar(SFG)places more emphasis on delving into covert types of language.Covert types,or cryptotypes,an idea initially put forward by American linguist Benjamin Lee Whorf,are those grammatical features that do not have overt morphological or syntagmatic manifestations.The founding father of SFG M.A.K.Halliday hailed Whorfs cryptotype as among the major contributions of twentieth century linguistics,and SFG draws on the notion of cryptotype to a great extent-as a result,many aspects of the English clause grammar are essentially cryptotypic.This paper recounts the history of how the idea of cryptotype was developed,reveals the fundamental feature of SFG as cryptogrammar,introduces the descriptive principles of SFG as cryptogrammar,and discusses how cryptogrammar can shed light on description of Chinese grammar from the perspective of SFG.