Abstract: 【Purpose/significance】It is of great significance to explore the dynamic mechanism of group emotion expression in the cri⁃sis, which can provide theoretical support for the guidance and decision-making of public opinion.【Method/process】This study ob⁃tains microblog posts and comments related to "herd immunity", and calculates daily emotional inclination and values based on the SKEP model.We construct sentiment series, and analyze the stationarity, randomness, and chaos of emotional series.【Result/conclu⁃sion】The research results show that the formation of public opinion is a process system.The group emotion expression is a continuous process of this system.At different periods, group emotion expression presents different dynamic characteristics.In the initial period,the sentiment series is generated by a random system.During the outbreak period, the chaotic system dominates the group emotion ex⁃
pression mechanism.The expression process of group emotion in the chronic period is a second-order Markov process, which is domi⁃nated by a stable non-chaotic system【. Innovation/limitation】This study explores the dynamic mechanism of group emotional expres⁃sion in the crisis, and enriches the theoretical perspective.However, this study only focuses on the crisis.In the future, we will study and compare the differences of group emotional expression dynamic mechanism between crisis situations and other situations.