 This study aims to determine the impact of the COVID-19 pandemic on public sentiment in mainland China by analyzing 64,723,242 posts from Sina Weibo and conducting a sentiment analysis based on natural language processing. The results show that the pandemic not only affected public sentiment during the initial outbreak but also induced long-term negative effects even in the recovery period, which were no longer correlated with the number of new confirmed cases or the post-pandemic economic recession. The study highlights the need for public health and government administrators to pay attention to public mental health even after the pandemic has ended. This article was authored by Hao Tan, Cheng Lanpeng, Chen Pingzhu, and others.