It’s been about half a decade since Michel Foucault delivered his famous inaugural lecture “Orders of Discourse”. Descriptive research into legal discourse, however, still predominates over the exploration of the hidden power relationship. This article aims to apply Foucault’s insights into discourse to the field of law and further shed light on the in-depth interactive mechanism of power and discourse. By investigating how legal norms were legitimized from the very beginning, it’s found that the legal compulsoriness and the compulsoriness of legal discourse are of the same origin.