This article synthesizes modes of representation in documentary films with strategies of legitimation. It develops a framework of documentary legitimation, where each of the six modes recognized by Bill Nichols in Representing Reality: Issues and Concepts in Documentary (1991) and Introduction to Documentary (2017) – expository, participatory, observational, performative, reflexive and poetic modes – tends to highlight certain legitimating strategies. For instance, the expository mode mainly legitimates through voice-of-God commentary, expert speeches and expository intertitles, the participatory mode legitimates through witness testimony and the observational mode legitimates through audience observation, and so on. The proposed framework is applied to a case study of a documentary entitled The Lockdown: One Month in Wuhan produced by China Global Television Network (CGTN). Analysis demonstrates how legitimation of the Wuhan lockdown during the early outbreak of COVID-19 is realized by adopting different representation modes and legitimating strategies. The article illustrates how an interdisciplinary approach may lead to a more comprehensive understanding of legitimation and its realization.