Interpersonal grammatical metaphor, as an important part of grammatical metaphor, is an incongruent expression of interpersonal meaning in mood and modality. Different language forms may result in the differences in transmission of language meanings. This paper investigates the linguistic significance of interpersonal grammatical metaphor's unconventional expressions from the perspectives of pragmatics, sociology and discourse analysis, aiming to explore the special interpersonal meanings and linguistic basis of interpersonal grammatical metaphor.