Metaphor is always a subject of central interest in the study of stylistics. But traditional stylistics has long focused only on lexical metaphor whereas systemic functional linguistics seldom extends to the stylistic function of grammatical metaphor, a term derived from the notion the form of the grammar relates naturally to the meanings that are being encoded (Halliday 1994: xvii). This paper seeks to go beyond and explore the stylistic value of grammatical metaphor. In functional stylistics, style is defined as a kind of prominence by systemically deviating the norms of the standard language. A natural corollary is that grammatical metaphor, as a systemic deviation of thecongruent lexi-cogrammatical forms, is of a certain stylistic value. Given such a working hypothesis, this paper first conducts a statistic analysis of the distribution of ideational, interpersonal and textual metaphors in 10 EST (English for science and technology) texts and 10 ENR (English news report) texts. The results reveal that the incongruity and deflection distribution patterns of grammatical metaphor are important criteria to differentiate one style from another. This paper proceeds to explore some properties of grammatical metaphor as a stylistic feature, including relativity, dynamism and fuzziness. In systemic functional linguistics, grammatical metaphor is defined in terms of forms, which are in turn defined in the three interrelated time frames of semogenesis: phylogenesis, ontogenesis and logogenesis. This suggests that congruent forms are relative, dynamic and fuzzy by definition and consequently that semogenesis is a process of metaphoricalization and demetaphoricalization. Now it may be rather difficult or even impossible to reconstruct the congruent counterparts for some metaphorical expressions. But this does not necessarily hinder the speaker/writer from using grammatical metaphor to achieve the desired stylistic effect. Given a more comprehensive statistic study of a larger corpus, we may have a better understanding of the stylistic value of grammatical metaphor and in turn a better understanding of the nature of style and a more solid prediction of the trend of language development.