With the process of reform and opening up, China's documentary creation has gradually moved from an exploratory period to a mature period. Both the creative concept and the theme content have undergone tremendous changes. As one of the important types of documentaries, political documentaries play an important role in spreading mainstream ideology and advocating the concept of political party governance. The research objects of this article are three Chinese political documentaries: He Shang(1988), The Road to Revival(2007) and Amazing China(2017). The reason why these three political documentaries are the research objects is that they represent the national ideology to a certain extent and have a wide range of social influences. The research method of this article is a mixed research method, which combines quantitative statistics and qualitative analysis. First, transcribed the content of the three documentaries into natural language; secondly, use the Chinese word segmentation tool to calculate the frequency and weight of natural language; third, analyze the characteristics of the three documentaries based on the frequency of the words; finally, analyze the changes of Chinese social thoughts over the past 30 years. In the conclusion part, this research believes that "He Shang" is not a representative of "national nihilism" and "historical nihilism", and has a strong enlightenment color. In addition, this study found that Chinese political documentaries on the one hand adheres to the tradition of reflecting on history, on the other hand, it is increasingly emphasizing political achievements. This study also believes that the changes in Chinese social thoughts are mainly reflected in three aspects. In economics, the development of "primary and secondary industries" has shifted to the pursuit of "technical progress"; in politics, it has shifted from emphasizing "secondary enlightenment" to the pursuit of "the rise of great powers"; in culture, it has shifted from "cultural craze" to "cultural conservation".