Abstract: The research on the evolution characteristics of network public opinion theme of sudden major animal epidemic events can provide decision-making reference for public opinion identification and governance. Taking the African swine fever epidemic in China as an example, this paper crawled the data of Weibo, mined the theme of online public opinion based on latent Dirichlet allocation (LDA) model, and explored the evolution characteristics of theme content and theme popularity. The findings were as follows: (1) The network public opinion of African swine fever epidemic events in China had roughly experienced four stages: initiation, outbreak, fluctuation, and long tail. (2) In the initial stage, the main themes of public opinion were pork food safety, the occurrence of the epidemic, and disposal measures, and the focus of public opinion management was to eliminate the communication environment of public opinion; the theme of public opinion in the outbreak stage was mainly pork food safety and pork price, and the focus of public opinion management was to stabilize social order; the theme of public opinion in the fluctuation stage was mainly epidemic situation, vaccine research and development, pig industry development, and pork price, and the focus of public opinion management was to enhance public confidence and trust in the government; the theme of public opinion in the long tail stage was mainly pork price, the recovery of pig productivity capacity, and progress in vaccine development, with the focus of public opinion management was to respond to public concerns in a timely manner. (3) The theme related to the development trend of the epidemic itself was a gentle theme, the theme related to food safety was a declining theme, and the theme related to epidemic prevention and control was a fluctuating theme.