Based on the modality system in systemic functional linguistics, this paper discusses the features of modality resources and their contribution to China’s national image construction in the English version of Report to the 20th CPC National Congress in a comparative corpus approach. It is found that the modality resources in the report are foregrounded with particular stylistic features. Different modality allocation strategies are used in different sections in terms of frequency, value and type, which construct the “true”, “firm” and “responsible” China’s national image. The research results are conducive to optimizing allocation of modal resources in the practical texts of political discourse and providing linguistic schemes for national image construction and the stylistic study of Chinese political discourse texts.