This paper analyzes the interpersonal meaning of different modal values in TED speeches from the perspective of the interpersonal function of Halliday’s Systemic Functional Grammar, using a self-built corpus method with 30 TED speech texts as English data. In English, modal values are mainly expressed through modal auxiliaries. By using the Antconc tool, this study finds that low modal values are used most frequently, followed by medium modal values, and high modal values are used least. This research expands the application of modal values in speech texts, helps speakers dynamically adjust modal values according to topic characteristics, balances authoritative guidance and audience autonomy, and provides insights for optimizing speech communication strategies and enhancing persuasiveness.