Voices on Twitter: Emotional and Thematic Responses to COVID-19 in Mainstream Media of China and the United States

International social media is often used to study global public opinion and has gradually become an important platform for global media to gain user attention and participation. The globalization of information dissemination has forced mainstream media in various countries to agenda setting and re-agenda setting on social media platforms again and again. This paper analyzes relevant media tweets about "China's COVID-19" on the X (Twitter) platform, focusing on understanding the attitudes and reactions of mainstream media in China and the United States to this global epidemic topic, and providing response strategies for the global information dissemination of Chinese media. Based on digital media analysis methods, thematic analysis and sentiment analysis of tweets from eight mainstream media in three years were conducted, and the content dissemination effects of the eight media were systematically evaluated. The results show that Chinese media reports emphasize the effectiveness of epidemic prevention and control, and the emotional distribution tends to be positive, while American media focus on social tensions and policy disputes and express more negative emotions. The results provide an analytical framework for understanding the information dissemination and discourse construction of Chinese and American media in the context of the global epidemic.