Nowadays, scientific analysis of language has a special place in the sciences, since the scientific methods give a better understanding of the texts. The emergence of forensic linguistics in recent years in Iran and the presentation of various approaches in this field has greatly accepted. This article analyzes a number of advisory theories of Iranian Justice Department based on the systemic functional grammar. One of the concepts in the systemic functional grammar is grammatical metaphor. Grammatical metaphor is one of the hallmarks of the language of science, and according to Holliday (2004) grammatical metaphor is of great importance in the development of scientific discourse and the advancement of reasoning in texts. Holliday has introduced and distinguished three types of grammatical metaphor, i.e. ideational, interpersonal and textual. The purpose of this research is to study the application of these types of metaphors in legal texts, to gain a better understanding of them. For this purpose, we examine the use of ideational, interpersonal and textual metaphors by examining about 20 advisory theories of Iranian Legal Department of Justice randomly. The results of this study suggest that legal texts have their own unique style and that the reason for applying such metaphors is to make these texts distinctive. Therefore, a better and more accurate understanding of these texts can be achieved with a closer look at the analytical tools presented.