This study aims at examining the definition about the congruency and metaphoricity of grammatical metaphor in connection with the Semantics of Legitimation Code Theory which stems from the notion of Grammatical Metaphor and Technicality of Systemic Functional Linguistics. Moreover, the relations between congruent form, metaphorical form within grammatical metaphor as process and semantic gravity and semantic density are explored. It is concluded that the system of ideational metaphor is described as weakening semantic gravity and strengthening semantic density, whereas the process of interpersonal metaphor is characterized as strengthening semantic gravity and weakening semantic density. The congruent form is exhibited with weak grammaticality and weak verticality, whereas metaphorical form is illustrated with strong grammaticality and strong verticality. It shows a legitimate strong evidence to explain grammatical metaphor’s congruency and metaphoricity.