Abstract: The spread of social media crisis events in the post-truth era has six characteristics:"high uncertainty, propagating pre-existence, emotional infectivity, subject diversity, instant interactivity and factual ambiguity". Communication dynamics research is an important means to explore the motives of these characteristics.However, at present, such researches mainly focus on systematic macro descriptions and lack micro analysis of accuracy. This paper takes the Hangzhou "nanny arson case" on Weibo as an example, and puts forward the dynamic mode of "information-value" communication, explaining how social media crisis events maintain their unique communication characteristics and continuous high activity from the micro level. It summarizes the utility of this model into three points:firstly, "group polarization" caused by emotional resonance detonates public opinion bombs; secondly, social media users in the post-truth era judge events by self-values rather than truth; thirdly, the input of new information in crisis events is often the competition of interests.