The governance policies have a prominent impact on the development and regional planning of the Yangtze River Basin, a key region for China to achieve modernization. Taking the public policy documents issued by China’s central government for the Yangtze River Basin from 1980 to 2022 as the research object, this paper introduces the NLP (Natural Language Processing) technology and semantic analysis methods to carry out quantitative research on policies. This study first examines the textual connotations of the policies and the characteristics of the policy changes based on the LDA (Latent Dirichlet Allocation) model to determine how policy changes occur for the governance of the Yangtze River Basin. Using the punctuated equilibrium theory, it then conducts two case studies in which the implications of specific major events are analyzed in depth. Research has shown that the changes in governance policies for the Yangtze River Basin are characterized by gradual changes and intermittent mutation, roughly divided into three stages: the stage of reform and development, the stage of transition, and the stage of prioritizing ecological conservation and green development. Moreover, such changes jointly result from three factors: the major events, the focus of public opinions, and the care of the central government.