Abstract: Since M. A. K. Halliday put forward the concept of grammatical metaphor in 1976, it has become a heated topic in the field of linguistics. The previous studies, however, still have not found satisfactory answers to problems such as the development, the classification, the generating mechanism of grammatical metaphor and its relationship with conceptual metaphor in cognitive linguistics. The present study argues that the development of grammatical metaphor involves three stages. The classification of grammatical metaphor should take into consideration both the functions and the strata of language.The generating mechanism of grammatical metaphori is mapping and blending between or within representational mode（s) in a clause. Grammatical metaphor and conceptual metaphor are to some extent the same linguistic phenomenon, sharing with each other a lot of features.