Nowadays, the analysis of interpersonal meaning in political discourse has attracted more and more attention from academic circles. As the ninth UN Secretary General to take office in 2017, to a great degree, Guterres is actually a symbol of authority, justice and fair, therefore his words have profound impact on the UN and the world. Therefore, based on the theoretical framework of interpersonal function in Halliday’s systemic-functional grammar, this article focuses on the discussion of Guterres’ inaugural speech from the perspective of modality system. By means of quantitative and qualitative analysis, this article analyzes the high-valued modal operators, the median-valued modal operators and the low-valued modal operators in Guterres’ inaugural speech, hoping to find out Guterres’ speech style and also explains how he realized the interpersonal meaning in his inaugural speech with the help of different values of modal operators. Furthermore, it also can reveal the relationship between the choice of language mode and the meaning to be expressed, so as to better understand the deep meaning in the speech.