This thesis chooses the theory of rank scale and the theory of meta-function in the framework of Systemic-Functional Grammar(SFG)to study ambiguity.It firstly analyzes ambiguities occurring at the rank of morpheme,word or phrase.Then it studies ambiguities at the rank of clause,from ideational ambiguity to textual ambiguity.This study shows that SFG can give a systematic and comprehensive interpretation of English ambiguity.