Grammatical metaphor in this paper refers to elementary grammatical metaphor in SFG, which concentrates on words' grammatical functions, and thus is completely different from lexical metaphor. Metaphoricity presumes an index that is gradated to describe the quantity of the grammar metaphor in a text. With two groups of college students' questionnaires, the positive study brings forth the following results: there is quite a difference between the two groups in construing congruent texts and metaphorical texts. Furthermore, the analysis shows that the metaphorical text helps subjects make better cognitive effects, and under certain circumstances, metaphoricity is in direct proportion to the cognitive effects and the relevance of the text as well. This is unexpectedly contrary to the common view that "the more metaphorical the text remains, the more difficult it is to be understood (LLBA, Adapted from the source document, Accession Number 200406133, (c) CSA [2004]. All rights reserved)